It depends. When someone is in the depressive phase of bipolar they might tend to overeat as a form of self medication. On the other hand if she is on medication many common mood stabilizers (Lithium, Depakoate for example) and all antipsychotics have weight gain and metabolic changes that make a person want to overeat as a side effect.
It depends on the medications. For me, I hardly eat at all. I drink a lot of whey protein shakes to make up for the lack of appetite. Some days are better than others. Yesturday I ate 2 roasted soybean (peanut butter substitute) and jelly sandwiches. Today, nothing. I can go days without eating. I'm not anorexic or anything like that. I do love food. I am just not into eating or sleeping. I do eat very healthy. All organic. I'm hyper aware of what I put into my body.
What meds is she on???