You sound a little muddled about it. Try  thecatsite.com   They are very good about cats.

Nonono maybe I wrote this wrong and didn't add everything.  She was completely fine with dogs, she doesn't attack all dogs.  She just attacked our old dog, who for some reason she did not like.  We have another dog, too, and she has never attacked him, and he has been around since we had the old one that she didn't like.  We have had Nellie for 2 years, everything has been fine, she only recently started doing this.

If we knew she did not like all dogs, we would have not done this.  She is fine with most all dogs, she never showed any aggression to our other dog.  It was only the one when he acted aggressive to her or her daughter.

All I know is that it is cruel to even think of putting her to sleep when she's obviously trying to "protect" her daughter, in her eyes...  and it would also leave the daughter cat without her mother.

I had two cats I had to have put to sleep for deadly illnesses (I would have never done it otherwise), and my cat that was left has never bonded with another cat the same way.  It is really sad...  she looked to one as a brother, and the other as her mother.  :/

I can understand how frustrating it can be when your pets do not get along.  We have a returned rescue who does not get along with our established hierarchy of cats.  We are trying to find a rescue willing to take him to be adopted out as an only cat or only with females, because we literally fear for our other cat's safety and the owner has shown no sign of wanting him back or finding him a home.

Anti-anxiety medication may help, I know some people strongly disagree with medicating animals, however, I think it is better than an animal being sent to be euthanized (it did not help this cat, but every animal responds differently). You may want to try giving your cat an area that is soley her own.  It might help her stress level, like a cat run or room where the dog is not allowed. 

For some reason your cat is feeling threatened, whether we understand why or not.  If all else fails rehoming one of the pets may be the only option to prevent injury.  It certainly isn't anyone's first choice, but sometimes it's necessary.  Good luck.

The reason can be simply the cat doesnt like or TRUST that particular dog. It doesnt take much for a cat to make up its mind but it is like moving mountains to get them to change.

It is not fair to kill an animal just because it cant deal with another animal it is forced to be around. At the moment I have a male cat who has taken to disliking 2 of my 3 other cats. He is getting better, but he was here first. Even though it would kill me I may have to rehome the rescue kittens because he cant deal with them.

My dog who gets along with cats doesnt get along with some other dogs.

I worked at the HSU for years and learned that animals are simple creatures.  They can choose to hate others of their own kind. They can choose not to get along with a natural threat. They can choose to hate people.

Im curious do these cats happen to be calico? Just a conversation I have with my vet.

And most important make sure it isnt medical as others have said.

She is technically not MY cat, my parents own her, I just live in the house.  This would be my parents decision.  I am trying to stop it by finding ways to cope with it.  I don't want to have to have her put to sleep, but my parents do because they do not know what the problem is and it freaks everyone out when she attacks.  They are afraid thaat there is going to be a day we come home and find blood and hurt cats and dogs everywhere. 

Nellie is not the problem, I don't know why this is being brough on her.  CUDDLES is the one attacking, while Nellie sits there scared to death and confused.  Again, we have had Nellie for 2 years, there have never been problems before and these just started.  If we knew Cuddles did not like other dogs, we wouldn't have got Nellie, but that is not the case.  I don't think she just has a dislike for Nellie, I think she is just waaaay too overprotective, and it's starting to get waaay too out of control where it affects the balance of our house and confuses all the other animals.

I can't respect anyone who would resort to KILLING their pet when the obvious answer is to either rehome the dog, or rehome the two cats.

This is disgusting.

If theyre that shy then she terrified of the dog.  Is she calico?

Intros are important when bringing a new animal into the house. Most people figure you just put  them together and let them figure it out.  The problem is that the first thing they learn and aren't likely to forget is what their perceived threats are. In my house intros take weeks. I never let any of them have a reason to be afraid of each other.

Cats are smell driven. My animals exchange smells from the time the are brought into the house before they even meet each other. I brush them with the same brush, wipe them with towels and exchange bedding between them. That way when they first see each other the smell is familiar. With cats after theyve been the house a while I also exchange small amounts of litter.
This all after making sure the new cats are healthy including FELV and worm tests etc.

My grouchy old man is finally coming around to the kittens. He has quit stalking them and is less likely to hiss and blap them when he sniffs them. They have not been left together unsupervised yet.  I wont allow him to perpetuate his dominance over the kittens and I wont allow the kittens to feel terrified of him.
Eventually he should recognize their scent and quit being so grouchy around them. `
I also make sure I dont punish or chase him when he is acting that way because then it will turn his association with the kittens into fear and paranoia and never get used to them.

If you cant resolve the issues with the mother cat. Find both of them a home together. Its not fair to separate them and they will adjust to a new home eventually.

Next time be more responsible when bringing another cat or dog into the house, killing one (which in your first post it was clear you were considering the option) is not the way to solve the problem.

 Making sure you have done your best to into them and then being responsible enough to take measures to prevent the fear of the new dog and then finding a home for one or the other would have been the best way to go about it.

It was irresponsible for you not to get the mother fixed in the first place. She was a stray kitten, how do you think she could have been spayed before you found her.
Are the mother and daughter spayed now? That could be part of the problem.

Well. Until about 3 wks ago it I thought it was only my theory that Ive had since I was about 12 (when I started working at the HSU).

Every cali Ive ever been around has been a little odd.  You know the pet me pet me then draw blood cats, the ones that stalk you and then maliciously  rip the skin off your legs and feet? The ones that you go to someones house you know they have another cat but you never have any chance of seeing it because it hides in the far corner under a bed in an unused bedroom the whole time the other person is there, only to come out at night to pee on the strangers belongings?
They have a tendency to be obsessive too.
Ive had siamese that have been a little odd but a calico is almost borderline psychotic.

I thought it was only my luck (for lack of better term) but one of the stray kittens I got is a torbie (calico and tabby). 

It had gone through my mind that it is a calico and figured the tabby would offset the calico. Still again hoping it was a theory limited to myself.

When I went to the vet and it came to doing whatever to the torbie kitten she started screaming bloody murder. 
The vet said "you know your going to have your hands full with this one its a calico".

My first thought was wow so Im not imagining that theyre kinda quirky. Then I said I figured the tabby would offset the calico she said I wouldn't bet on it. 

So I guess well see. She does seem to have a few quirks like licking until your raw but as long as it isn't followed up with a good chomp then I cant complain.

That's the thing, she is not terrified of the dog.  Any other time she will come out looking for attention and not bat an eye at them.

She, I believe, is a tortie.

I've been reading this whole thread and I have to say, everyone is being pretty judgemental of Ktina, here. It was irresponsible to not get the cat spayed, yes, but she's 16  now and got the cat 7 years ago. When she was 9. I would imagine that it's not her fault that the cat didn't get spayed. Also, I agree, it's awful to think a cat would get killed for behavioral problems. If it was a dog, the owners would take it to obedience school and that would be that. Cats are a little trickier. But, again, Ktina could have just agreed to let her parents put the cat down instead of coming on this forum to look for solutions. So instead of judging, we should help out. I know a lot of people already did, so I'm not saying that no one reached out. It's just that some people are not experienced pet owners and they need some guidance from those of us who are.

Anyway, I had 1 cat who lived alone with me in our apartment, but my dad had a dog so when I picked out my cat I made sure he was being fostered in a home that already had dogs so the scent on me would not scare him and also if I was going on vacation my dad would be able to take him. It just so turned out that after a few months I had to move to a place that didn't allow pets and my dad did have to take my cat in. Needless to say after a slooooooow introduction, my dog and cat were very best friends for years until my dog died. Then, he was really depressed because he lost his best friend. At this point I was living with my fiance who has 5 female cats. I had been reluctant to take my cat with me when I moved because I didn't want to separate him and Sam (my dog), but I thought the companionship would do him good since he was all alone. I was extremely nervous because he had never been around other cats before, as he was a rescue and hand raised. It was a very tense few weeks. I had to keep them separated at first and they would only be allowed to be in contact under supervision. I would exchange litter in their boxes and leave out tee shirts for the cats to sleep on which I would exchange regularly. When the supervised visits started going very well, we let them all out together for a full day, which was a Saturday so I was home all day to "observe". As things kept going well, they stayed together and now, 1 year later, are all the best of friends. I think maybe your dog and cat were not properly introduced at first. Have your parents taken their cat to the vet? Or did they just throw their hands up and give up? Sudden changes in behavior is often the only sign you will get from a sick animal. You should sit down with your parents and explain to them that you don't just euthanize an animal because you don't like what they are suddenly doing. Part of being a good pet owner is taking your animal to the vet and I think that needs to be your first step. Also, maybe you need to keep the animals separate for now, until you can find a solution. My fiance had a cat that was feral and very sick when he took her in. She would attack anything that moved. What he did was get a small dog crate and whenever the cat would attack she would have to stay in there for 15 or 20 minutes. She HATED that crate, so eventually, she stopped attacking. Now, she's the sweetest, mushiest cat EVER!! Good Luck!