Honestly not trying to be mean but the only appropriate way to bring it up is to either a) not or b) if they cause her problems 

And I intend no hate but if she has not displayed any displease with her body then please don’t make her feel self conscious about it because it’s unnecessary. If they’re fine and she’s fine you’ll either learn to love them or it’ll be a deal breaker in either case what’s meant to happen will happen. 

Don’t ask her to physically change just for you cause that’s extreme, if she does it then something happens and you guys aren’t together then she’s stuck with what you wanted and it’s not fair. 

Good luck I wish you the best