She’s in a Pavlovian response type situation where her gaining makes you happy which subsequently makes her happy and in some way is tabooed from her mom’s body shaming growing up. She resents her mother’s criticism because she always felt alienated by her mother’s comments and feels empowered because she found someone who lusts a curvy more fuller body. Thus, gaining is empowering to her because it proves her mother wrong and justifies her resentment. However, she’s going to reach a point where she gains so much that it interferes with her current way of life and she’ll then have to choose between being fat af and having a normal life. Make sure she doesn’t reach that point by supporting her and making sure She’s happy with her body and herself, because ultimately that’s really what the goal of body acceptance is. It’s not about being 500lbs or being 80lbs, it’s about accepting yourself for who you are and not about the superficial comments that other people make.