I hate to say this, I don't mean to sound rude or anything, but keep your cat and do not let that devil child into your home!!!! If that child, not your stepson, can not treat your animals with respect, than they should be banned from your home. Star was in your home before this rude kid started tormenting her! If the child's parents do not discipline their child and teach her how to treat animals, then they should be told their child is not welcome into your home. This cat attacked because that child has put fear into her! The reason Star attacked is quite simple. It is called REDIRECTED AGGRESSION. The child that torments this cat has caused this problem, it is NOT the cat's fault. That cat has had enough and is now letting it's agression out on someone else. If you put this cat into a shelter, more than likely it would be put to it's death. No one will want to adopt a cat that attacked a child, even though it is clear that the children were the root of the problem. If I were you, I would put Star in a room that is off limits to any child when they come to visit. Let the child's parents be aware that if their daughter goes into that room, they will be told to leave. Your baby will be fine once Star has had a chance to get over her fears. As for your stepson, even though he loves animals, he will just have to understand that at the moment, he will not be able to play with Star. Yes, I would also take Star to the vet to see if she has any injuries. Your so called devil child may have injured Star, she may be in pain and is showing redirected aggression due to the pain. Throwing the cat was not a good idea either.
If you could find the cat a good loving home with no kids, that would be good too. But why should you have to give up your cat and why should the cat lose it's home, just because there is an irresponsible parent that does not know how to discipline their child and teach her HOW to treat animals. This child is going to be abusive to all animals if her parents do not teach her now. I know one thing, if a child comes into my home and abuses my cats, I would have swated that child's behind and then told the parent to remove their child immediately. I know this is hard for you and I am sure it was a terrible situation, but it is not the cat's fault. You said it yourself, "She hasn't scratched or bitten since she was a kitten". Please, take control and put your foot down. Do not welcome into your home anyone, including any child, that can not treat your cats with respect. Once the tormenting stops, Star should go back to normal again. I am not trying to sound or be mean to you, I know this is hard for you, I just feel bad for Star, it is not her fault. To me, my cats are just as important as any child or adult. I would not or will not give them up for any reason, that is, unless I lost my ability to give them the proper home.