The resources for your own pets are primary.
In terms of her behavior, many if not most "friendly neighborhood cats" (though by all means ask all around if you can) will probably be less shy than she is. It sounds like she's been pretty much on her own a while though, being a domesticated species, might well know that NICE people she can trust could help her.
If you are rural, then I'd understand trapping, med help, release...especially if you can do it affordably. And if she's skinny, I'm guessing she might be fending for herself...especially if you see her seeking shelter from weather and such.
If you can find (internet is a great thing...as well as calls to vets and rescues/shelters...though they all agree with leaving cats feral) a feral cat program in your area...or even one who isn't close for some advice, it's a good thing.
The tough thing is that once you start feeding her, if anyone should move, etc...she'll be dependent on you and probably won't want to move, too.
Getting her spayed, and hopefully with some shots and all is NEVER a bad idea, if you ask me. Otherwise you may have 8 cats sleeping under your shed, and an already skinny mom is probably not the best candidate to care for them all, find food, AND breast feed them all.
Good luck with her. And best to Kiki,
PS: If it gets cold where you are, and she seeks the truck for refuge, do know that cats will sometimes crawl up into the engine area or on warm tires...so be very careful and probably inspect as bad kitty accidents happen a lot from that.