OK I am sorry, but there is something wrong with a woman who is attracted to morbidly obese men. Granted, people should look beyond a person's exterior, but when it becomes the attraction first (which in her case it seems to be)...I would say there are...no pun intended...larger issues in play.
I wish them the best, but will she be happy if he loses the weight? I am glad he has a goal and is working towards a healthier life...but I still say something is off with her. Can't put my finger on it exactly (she probably can't either, just saying).