Hello. I'm Dr. Autumn and I'm happy to work with you on this problem.
Wow, what a difficult situation to be in. It sounds like you have really tried to be understanding, based on your friend's history. And, I believe that your interpretation of the situation is spot on. It sounds like she is feeling insecure, and she is trying to feel better about her own situation by mocking you. If she can tear you down a little bit, then she can feel better about her own situation. This is not surprising at all, given her family history. This is probably a pattern that she has lived with for much of her life, and it sounds like it continues to repeat itself with her sister. It sounds like her sister behaves the same way, tearing her down so she can feel better. However, while it is important to consider her history when you are trying to understand her, it is also very important that her history does not become an excuse for her mistreating you in any way.
It seems like you have been really thoughtful about how you want to respond to your friend. I think your planned response sounds like a good response. Another thing I might consider is talking to her about it at a completely different time. It sounds like she is pretty defensive about her own eating habits. So, she might be very defensive about the entire situation if you discuss it after a meal. Especially if her emotions are pretty high, she might not hear your statement the way you intend it. But, if you mentioned it at a different time, that's not centered around a meal, maybe she would be more open to hearing about it. That being said, you obviously know your friend better that I do, and you should trust your instincts about the timing of the conversation.
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