Aww hun... my heart goes out to you about your cat, i dont blame you for not being able to do it, I dont think I could either. . I feel like crying for you right now. Is your cat in a lot of pain, did the vet say theres any way you could keep your cat at home in a way that it doesnt have to be in pain (maybe she could give her something to help keep her comfortable) and that she can stay at home until she passes naturally?