It blows that you had to deal with that, but I don't think it's fair to assume from a few paragraphs of prose that her experience is exactly congruent with your own.

My own approach is to try talking first. She mentions she's 24, and implies that this is her first "serious" relationship. To me that means the man in question is young enough to be really stupid without necessarily being totally set in his ways. There's the potential for improvement. (You'll note that, even in wag mode, I never call the girl tubby or the man correct. What he did was stupid and wrong, and not just because of the rules of American culture concerning "the fat talk".)

The letter writer also gives evidence that this a new thing, not something she's been living with. If it's been something she's endured for awhile, my suggestion would be to get some space. You don't make smart decisions with your closest companion tearing you down. You need to open up a gap so you can hear yourself think.

Oh, and if he expects her to keep it off after they're married, he's an unrealistic asshole, and should be beaten into unconsciousness with a sackful of rabid weasels. I probably should have included that caveat in my first post...