I think it's totally unreasonable to get rid of the cat (who has been in the household for much longer than the child) because it scratched when provoked. It's an animal and that's it's natural instinct to protect itself. It would be very unkind to try and rehome a cat of that age (or any age really), part of having pets is learning responsibility about caring for them well and treating them kindly which your DD will eventually learn.