I'm afraid not many Therapists are experienced in dealing with emotional eating and body image issues. Eating disorders are wide and varied, and aren't just about anorexia or bulimia. I think you need to be assertive with her and say that diet tips are not ok.

Have you read 'fat is a feminist issue' or 'health at every size'? Those books are great for explaining emotional eating and gentle ways to help us through. I've heard really bad things about over-eaters anonymous.