[cypher]

I'm not sure how you can persuade you Mom to get a cat if she's really against it, she is right to be scared a cat would eat the hamster though, if you did get one you would have to be sure it could never get into the room where your hamster is, even if it couldn't get into the cage just the scent of a cat is extremely stressful for a hamster.
Maybe if you can show you've considered things like that & maybe explain that cats are actually really fastidious about keeping clean & would be sure to wash their feet after using a litter tray you might stand a better chance.