At first, like Camryn, I'd fly mask while she enjoyed breakfast and she "seemed" fine with it. Then she began pinning her ears making "mare face", I chose to respect it as I could understand not being messed with while eating.
Then she began pinning her ears and snaking her head at me as I fed! While I get after having come to us very thin, food was very important to her. It's not something I find acceptable for any reason. I began keeping her back and away from her feed with my stick. She now turns her head/shoulder away now until I give her th OK, if she doesn't, it's "outta the barn girl." Of course I have my stick in hand still. This may or may not be part of the reason she's been leaving the barn as I enter? Cure one problem, start another kind of thing right!
I informed her yesterday (tears involved) that she had a narrowing window of opportunity to decide what if she wanted to stay.