The thing that's critical is to never have the mindset of trying to convince. First approach would be to open a line of communication. What you don't want to do, is get to a point where she feels pressured. Doing so can lead to possible resentment or her doing it just to shut you up. What's worse, is her getting into it even by ******* then maybe liking it too much for your taste. Then guess what? Ain't ******* you can say, and if you did, she won't listen. But ask yourself if your fantasy is worth the happiness.