Mares get periods? Or did you mean in heat?
I think jmike is right, she knows she's boss. What do you do when she pins her ears? Stop? Back away? Run and get the carrot?
When you give her the carrot you are rewarding her for pinning her ears.
When you have a carrot and she pins her ears when you are coming, or if you don't have a carrot, make her move. Make her back up, yield, make her move her feet and act like YOU are boss.
Think in your mind "I'm sick of your attitude, now MOVE IT!"
Do not give her praise or a treat until she does what you want her to do and she stops pinning those ears.
You should probably go work on respect from the ground.
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