How can I get her to say yes?

"Are you really going to put your selfishness over my own well being? You're my mother. You're supposed to want what's best for me." That's what I'd say.... but then it's also really harsh and will probably just cause her to be mad at you thus making the whole situation worse.... It'd probably be better to get some outside help by getting other family members such as your brothers or dad to help convince her.