Gingerbeard:
None of the options really work for me. Probably closest to B, 'cause I'd stay for sure.
It'd be less compromise, and more "what do you need to do and what do you want to do as a result," and then me accepting her plan of action 'cause her happiness is more important than a number on the scale.
Besides, it'd be a very odd health issue for her not even remain chubby, which I expect as a happy feedee she'd want as a minimum for her own comfort.
I know Ginger, it would suck anyway but as someone else has pointed out it is hard enough to find mutual love+same fetish. Oh, and live in the same city!