With friends like that you don't need enemies.This is petty period and immature on her part.
You lost a person who didn't deserve the title "friend" but you have all of us, who really ARE your friends.
Newsflash for her: Your child is going to have to learn to live without, eventually. Saying no once in awhile won't kill him.
Personally I would have never let them get away with keeping the cat in the first place, and if it was something the police couldn't have been brought into than I would have never spoken to her again. You're too forgiving, I hope karma gets this woman.