This seems inappropriate to me. I don't really see why it would ever be appropriate to yell at a client, honestly. Like unless there was an immediate danger or something, but that seems like a situation that could call for deescalation at that point anyway. Being firm is one thing if they are concerned, but not yelling. It also seems super irrelevant that you are drinking a Gatorade and I do not know why it would make her so angry. If she has a problem with you having food in session, she only needs to tell you that she finds it respectful. If she thinks you are making overall bad choices for your health, then discussing the root causes might be a good idea in therapy, or suggesting you see a nutritionist. From your further explanation about her recent weight loss, it actually would seem that she has too much focus on food/weight herself and needs to address that in therapy or something perhaps to figure out a way to not bring that into session. I mean for all she knows you could be struggling with weight, food or body image and as someone recovered from anorexia it upsets me that she would bring that up in such a negative way.