Thank you guys for your input!
I have given this a lot more thought and I don't think I will do counselling just yet. I like the idea of having just one at a time in the room with her. I don't know if she is being shown how to do it or just told, it was my understanding that she is just being told though. I will discuss this more with him. I do hope he downsizes the number of these kittens though because I just think it's too much for a 1 bedroom WITH a hyper child and at this point in our relationship we can't afford the conflict this is causing already.
Annie Brooke is right. Your daughter could be angry inside and not know how to express it and at 5 certainly won't know how to deal with it, and this may be why she is acting out by being too rough with the kittens. I think counseling is an excellent idea.
Try it. When a child acts out with animals, you have to be concerned that she might hurt them, and if she does, you'll have to wonder if they are a substitute for other things in her life that she would like to be able to affect and cannot. I'd talk to a children's therapist.