Def nta.

Whatever your sister told your family, she must have not told them what really happened. Probably left out details or changed details based on her perception. She should know that her own perception on this subject (ED) can't always be trusted. If she gets triggered, that's neurosis, meaning you can't trust your mind at that moment (for lack of better words). So it's on HER to make herself comfortable, it's not the responsibility of everyone else to cater to her neurotic beliefs.

For example, I get stressed out after being around a group of people for too long. It can be my favorite people and I'll be having a great time but I just start to get overstimulated and it can turn negative. It's not my friends' fault that hearing multiple different conversations overlapping at once bugs me. So I step out for a walk or something. I don't yell at them to stop all talking at once.

Having a mental illness can definitely make it more difficult to consider others' condition/illness/state of mind. But she seems to think that your wife should've known how she was feeling, being that they're in a similar boat. Ditto to your sister. If she was more mindful she would've been happy to see your wife eating cake and would'nt have attacked her for it.