Don't make it your problem. people with eating disorders do NOT want people poking their noses into their business where they're not wanted. So if you want to remain in some good standing with her, ignore it. It may not be healthy, but emotionally that's what I think she wants. When she wants help, she'll get it, or she'll just grow out of it and mature like many girls eventually do. ED girls hate all this sneaking around and telling people behind their backs. Don't take it personally, but if you really can't stand to be around her idiosyncracies, changing roommates is your best bet.