The anorexia....oh gosh. I don't really know how to give you advice with this, but I had bulimia through my first year of college and those dining halls are bad news bears. It's unlimited, unrestricted, guilt-free access to all your favourite foods. I know at my university I was allowed to get a refund for my meal plan because I couldn't control myself around the buffets. I did much better when I could do my own grocery shopping and just stock the fridge with healthy, moderately-sized choices. With anorexia, the big recovery focus is getting over fear and restriction of calories/certain foods. So it's actually great that she can eat desserts now. And with the weight gain, I've watched a few friends go from skeletal to slender in ~6 months, then to stocky in the next ~12 because recovery is a process and their bodies are resetting and they're learning how to eat normally again. But you make it sound like she's already recovered, but is eating in excess and ballooning in weight, which sounds like binging. And since she's undoubtedly noticed that she's gotten fat, I can see purging or caloric restriction coming up in the near future. Especially if you bring up her weight, no matter how nicely you say it.

Sit her down and say that you're worried about what (and how much) she is eating, because it's changed so drastically. Tell her you're worried about her mental health, because of the low self-esteem and jealousy etc. and ask her if she's using food as a coping mechanism/release. Maybe agree on some small healthy changes, like go on long walks together and cut out desserts. Start cooking healthy meals together and get her away from the dining hall (the semester is almost over anyway). Or maybe get her to go and talk to a counselor about what she's going through, if she agrees to that.

And if you do end up splitting up, call her parents and explain your concerns. They can watch out for her and know what to worry about.