Recovery is hard

I've been in recovery,but the idea of weight gain is still constantly on my mind. A lot of my self image issues stem from stuff my sister said and did to me as a child. The worst part is she doesn't understand and when I try to talk to her about what hurts me she laughs because it's funny to her. Anyway, I got help right after she went to college, and I've been making a lot of big strides towards overcoming my mental roadblocks. Yesterday, Christmas, she wanted me to go with her to play tennis but I wasn't in the mood. She got really mad and started insulting me by calling me lazy and telling me to eat another dozen Christmas cookies. I tried to tell myself that what she was saying wasn't true but part of me believed her. Since I struggle with anorexic symptoms (since I'm not underweight I don't count) and have been diagnosed with bulemia I have a lot of trouble telling where the line with food is. What is the difference between a binge and a cheat day? What is eating normally and what is starving yourself? What if starving yourself is normal? How do I achieve the body and health I want if everything I do involving food is wrong so far? How do I get healthy if doctors are afraid to tell me what a healthy diet is for me? Why don't I get to control what and how I eat just because I'm under 18? By that I mean I am just forced to eat what my parents put on the table and I have no say. Why is everyone afraid to help me understand food when I want want to get better?