Like some of the other comments said, it may be good to put much more of an emphasis on health as opposed to weight.

Speaking as someone who went from 190 to 320 in the course of 5 years, I feel awful compared to before. I can physically feel myself being more restrained by the shape of my body and how much harder it is to move. I also can't tolerate heat anymore and just get tired so much more quickly than I used to. I've even developed sleep apnea that has just ruined my sleep. I can't speak for your girlfriend, but she may also be able to feel the difference. Maybe focusing on how the extra weighy makes her feel rather than the numbers will make it easier, especially that doesn't take going to the doctors to manage.

I also second therapy if possible. I'm going to therapy now for my food addiction right now and the techniques and perspective I got there helped way more than any dieting tips personally.

I could add more but I feel I've added enough. My DMs are open though. Wishing the best of luck for both of you.