My sisters hamster attacks anything near his cage besides my sister. Why? She also hates rats.?

Why does my sisters hamster do this? My sister put the hamsters cage outside with it in it. I let my rats meet the hamster through the cage bars. Then the hamster all of a sudden hissed and tried to pounce at my rat through the bars and scared the heck out of it. The hamster does it to everyone but my sister it even scared the cat to death. I know they are highly territorial but I have never seen one like that. When we first got her I tried putting treats in my hand and it bit me. Then my sister tried and he ate it and allowed her to carry her. For some reasons she also hates my rats. When my sister was holding him today and went in to my room her hamster jumped out of her hand and bit my rats tail that was sticking out. Why is she acting like this? And do all syrians act like this? Also do hamsters usually hate other rodents?