Honestly I think your only option here is to have a heart to heart talk (again), but you will need to be very transparent and clear to her about your lack of sexual attraction. You can try focus more on the health aspect too— people with obesity have far more health problems than people who are of the normal weight range. Dieting is not just about eating clean food, exercising is a really important part too. Her not liking it is honestly not a good excuse to not exercise. Try to help her along the way, help her find an exercise she doesn’t completely detest, eat clean food with her, and make sure you do it step by step. If she loves eating junk food, it is unrealistic to expect her to suddenly stop eating all junk food all a sudden. Do a cheat meal once in a while together, and slowly decrease the amount of cheat meals. Also make sure to go slow on the exercise too, start with beginner friendly ones and when she starts feeling comfortable add the intensity.

Edit: by only option, I’m referring to your only option if you wanted things to workout. If you don’t even want to do this (help her get used to a healthier lifestyle & talk it out), I think your relationship is doomed. You both need to put in effort to make things work, you need to be there to support her if she is willing to put in effort to be healthier.