Sassy felt threaten by the new commer. Sassy had to hold her ground. So did the cat. Now Sassy's in monkey heaven. And the Cat is doing time behind some Zoo cage.
Most animals feel tuff around kids.
This includes domestic animals like Rockwillers, and pit bulls, maincoon cats, boway constriters. That's because they feel big around smaller humans. That's too bad that cat acted that way. That would have been a great pet to have. Small, agile, easy to train.