Why not get two little ratty babies?  Then the little ones can keep each other occupied when they're feeling frisky without irritating your older girl, and when she passes they will still have each other.

Thanks RatAttack. I let her smell Phe's body before I buried her... I know they do that with horses so I thought I'd give it a try. She seemed like she was upset, but understood.

Do you think my cage would be big enough for three? I don't have a picture, but you can see it pretty well in this video I have:

http://www.youtube.com/watch?v=k8iIZlAriXM

I agree with getting 2 younger rats, siblings preferably.  As for the cage, I have the exact same one, and it will not be big enough for 3 girls.  Since Petsmart stopped carrying the one that would best suit the number, I suggest going there or Petco and see what type of larger cages they have.  If you plan to keep rats for a long time, such as having them as lifetime companions, people have enjoyed Ferret Nation cages, and Martins cages, both of which can be found online.  I did see a nice ferret cage at Petsmart, 2 actually, but you have to make sure the bars are no more than 1 inch apart, and these cages are somewhat expensive.  There again, Martins and Ferret Nation cages aren't cheap either.  There are cage swaps you can do with other people here, and I think there is one at http://www.rmca.org.
The cage you have right now will work for the 3 until you have a new cage, but I would get the new one, or order it shortly after getting the new girls.  Have fun finding your new little ones to keep you and Tilly company, & make sure you get that bigger cage. 

I made a mistake, RatAttack is right about the half inch bar spacing.  My apologies.

Try going to http:www.ratster.com they have a list of breeders, there might be someone near you.  Also, don't be afraid to go to the humane society or a rescue.  There are many rats out there looking for a forever home, and breeders only have about 2 - 3 litters/year.  You can make a difference in a ratties life.