Kelly,

you certainly did the right thing. I personally believe that this person does not know anything about animals. Yorkster is right there is no way of knowing which cat killed the hamster, I had a cat once that was born indoors and never went outside once in her life but she still tried to kill any bug in sight. It's their instinct after all. It's like trying to turn a tiger into a vegetarian! Not only, but punishing the cat days after it happened is absolutely crazy, the poor thing will never understand while she is getting punished for!

She has every right to be upset about the death of her hamster, I certainly would be (I'm the person who got terrily upset when I crushed a snail in the dark ), but she should also realise that if she decides to keep to breeds which are not stricly "compatible" it's up to her to keep them safe.