Sqad's suggestion of a psychiatrist is probably the way to go, but only if she is amenable. It sounds like she is eating to compensate for something (assuming that there is not a medical problem, which should of course be ruled out first). Apart from puberty, has she experienced any changes in her life recently? Has she got friends and a social life? She may well not accept help from her mother, as her parents may be part or all of the problem, but she does need to stop bingeing before it becomes a habit she cannot break. Size 12 (if she is of average height) is not huge, but she will get bigger if she carries on. I speak from bitter experience here. When I was 13 my family moved and I had to live in a small village with no friends, very strict parents who controlled my life to the extent that I had no opportunity of meeting anyone outside school and nothing much to do except stuff myself with food. But since nobody did anything to stop me - in fact I don't know whether they even noticed - it took me half a lifetime to sort myself out. It's good that this girl has people who care and want to help.