Throwaway because reasons.

My best friend is fat. Due to a number of health issues including PCOS and breaking her leg in multiple places a few years ago, she hasn't been able to properly exercise in some time and has gained more weight than she would prefer. She knows she's fat and is trying to increase her mobility/etc so that she can get some more exercise and lose some weight. That's not the issue here. 

Earlier today she had had a fight online with a good friend of ours and she'd been really upset about it, and I'd taken a few hours out of my work day to help her sort it out (she didn't ask me to, I chose to, and I have flexible working hours).

Tonight she was in a bit of a self-negative spiral about how she was a terrible friend &amp; she'd made me lose hours of work etc. This isn't an unusual thing for her, she has depression and often needs to be reassured that things are okay. It was a long day for everyone though and when my reassurances that I was responsible for my own actions and she wasn't a terrible friend, etc seemed not to be getting through, I got frustrated and said something like "can you get it through your stupid fat head that you're not responsible for my actions!"

She was pretty hurt by that, and she explained later that while it's no secret that she's fat, I had never used it in a pejorative sense before. She was right and I apologised, but she's now doing things like trying to pretend she's not hungry because of it, and claiming that I didn't do anything wrong (by calling her fat like that).

tl;dr: I called my overweight friend who struggles with self-esteem fat at the end of a difficult day, and now she's showing signs of disordered eating and claiming it's all her own fault. AITA?