In the first couple years of me dating im2smrt4u I gained about 35lbs. I was overweight to begin with but so was he and he enjoyed spending time with me. I didn't really think too much about my weight even as I was getting bigger. I was able to ignore it because someone loved me and was willing to be naked with me.
At some point around three years, my weight came up in a bad argument and it devastated me because he had never mentioned it once before. It came out in a very bad way and it hit me harder than it would have if he was like "hey we both need to lose weight lets do something about it", or "Im concerned about your weight, do you want to work on getting healthy together". Basically I would have had an easier time with it had he tried to help me the way you have tried to help your girl. But no matter how nicely you tell someone they need to lose weight, its still hard to hear. It took me a long time to be completely comfortable around him again. I dropped about 20lbs and pretty quickly. He told me he felt terrible about it, and some time later when I asked him about it again he said he was stupid and immature and realized what was more important to him was me.
Once we started at the university I gained so much weight that I was at my heaviest. He never said a word, if I asked he said he had no room to talk and if I wanted to lose weight I would just look even better. (Also keeps telling me if I lose my boobs hes gonna "fatten me back up"
) About a year and a half ago I decided I was terribly unhappy with my self and dropped 30lbs. I have kept it off but I wanted to lose more to get to my ideal healthy weight so for a Valentines Day gift to myself, this year I bought a gym membership.
Its gonna take time for her to feel okay around you again and while she may be unhappy with how she looks, the thought of her losing all the weight shes gained may seem a bit overwhelming. (I had 50+ lbs to lose at the beginning and there were days that I thought it was useless)
All I can tell you as advice is keep making her feel sexy and special. When she is ready to lose weight be as supportive as you can, go to the gym with her, help her plan healthy meals and reward and encourage her progress and success. Help her set reasonable goals, not just losing the weight. When she loses 5-10lbs treat her to a mani or pedi.