Aw, poor little gal. At least she had someplace secure and comfortable for a little while.

I don't think anyone else mentioned this - you definitely didn't starve her! It's true garter snakes won't eat crickets, but it's also true that they can go weeks without eating, even in the summertime, so three days wouldn't have hurt. It sounds like she had some bad injuries, and they must've gotten the better of her.