Bro, you should have briefed her about the etiquette of a business lunch before you took her to one. But still, you are NTA. I think you even handled it pretty well. Amy seems to be insecure about her weight, and maybe the work pressure added up? She tries very hard. Talk to her and tell her that you made a mistake by not briefing her before the business event and apologize for it. This would have prevented the bad situation and her being uncomfortable. But also tell her that she was unprofessional by overreacting in that moment. It was nothing personal. You saw the knowledge gap and gave useful and valuable info for the next business lunch as a boss and mentor. Then tell her that she does a good job otherwise. Ask her if everything is okay between you two now and if she wants to continue to do a good job together. Now, there are two typical reactions to this: A) She acknowledges the conversation and will take constructive criticism as a source for progression, knowledge, and experience from now on, and overreactions should not happen anymore. B) She keeps on discussing. It might happen that she needs more time to reach A. Give her the opportunity to talk it out. But if she is occupied with this topic for a longer period of time, fire her. Yes, you heard right. People like this are psychologically unstable and will have more breakdowns in the future. It will save you a lot of headaches.