LondonFA:
She was beautiful before she gained, but now (and maybe I'm a little biased), she is the most stunning woman I have ever dated. And she is well aware of that.
Of late however, she has started to retort (in a lights hearted manner), "you're a liar, but thank you".
Last night we had a long conversation of her asking me how she could know I was telling the truth about my preferences. A lot of ideas that must be mixed in with her decision came out such as the idea that men who claim to liked fat women do so because they believe others won't find them attractive and hence won't stray.
It's quite the minefield especially as she was comfortable with her body until recently.
I hope she's resolved some of those conflicting thoughts and feelings -- cognitive dissonance can be exhausting!
One thought, if she is still struggling, is to help her have something else that will draw attention and praise, so that people are not first focused on her weight. With people she knows, maybe taking a new class or training? For just general being out in the world, especially for dealing with other women, sometimes a luxury can help. A designer handbag, a stunning pair of earrings or a glittering finger ring, or even new hair done from a high end salon that does a great job.
Also, if you don't already, go shopping with her, ask her to come out of the change room to model for you. Choose a couple of things more daring than her usual for her to try on. "Not those shorts, they are toooo short!". "You don't have to buy them, but I reeeeaaallly want to see you try them on.". It is a good way, IMO, to help prove that you adore her current body. Words are nice, but finding ways to SHOW it really helps.