This. Her behaviour with the fries shows severe MENTAL problems. She's not only going for comfort food, she's also going for alcoholism! Regardless of what she told you about her being happy and "I'm able now to let myself go", fact is, no normal person does what she did with the fries. That was compulsive behaviour, and it requires deeper knowledge than either you or anyone here has (any psychologist among the shitpeople here?).  Seriously, the fat is not even the worst thing. It's just a result of the mental problems. Take her to a therapist. If she refuses, cut all relationships. She's going on a downward slope and you don't want to be dragged down with her. One abuse is bad enough: two together are heading for disaster.