I would not. Being a mother myself, I would say err on the safe side. Even a Dustbuster would be a safer choice, and that’s a risk I would not recommend taking.
Get her something that tells her you think of her as interesting, or glamorous, or deserving of luxury, or fun, or precious, or wonderful, or brilliant. But not fat. That is no gift. Even if it’s true, that is not what you want to reflect as your dominant perception of her. She’s your mother no matter what size she is.
Sometime later, you might tell her that you are thinking of getting an exercise ball and ask her if she’d like to try exercising with you.