Kitty is the only one being aggressive so I'm just keeping her away from Alexis. I'm not sure what else to do. Kitty has been through obedience school already so I am clueless.

The bad thing is Kitty is 7lb and Alexis is 3lb. Kitty has seriously hurt Alexis to the point that she needed the vet and antibiotics. I'm just too scared to put them back together. I don't want Alexis hurt anymore.