15 pounds ain't that much. If that is enough to change your opinion of her, you may need to reexamine your standards. It sounds like you really care about her, so the best thing you can do is try to sympathize, and not try to solve her problems. It took me over 15 years of relationships variously crashing and burning before I figured this out. Women don't want men to solve their problems. Listen to her, sympathize with her, support her, offer to do anything she wants to (go on walks together, biking, diet, whatever).