Mare being a huge brat!
So I took one of my mares last weekend and dropped her off at my friend's house for her to ride for a little while, since I am very busy with school and work. My friend already had a mare at the house, and she and my mare hit it off. The day after I dropped my mare off, my friend went and picked up her husband's weanling filly and brought it to their house.
Every chance she gets, my mare attacks the filly. She will corner her and just beat on her with her feet. This is a normally very placid mare; of the adult horses in my pasture, she is at the bottom of the totem pole. She was pushy with the yearling filly out in a separate pasture, but nothing like this. My friend has had to keep them separated so that mine can't get to the baby. If this keeps up, I'm going to have to go and pick her back up, because it's not fair to my friend or the filly- and I really don't need my mare seriously hurting the baby.
Any thoughts on why this is happening or what can be done, if anything, to help her get over this random rage? My mare hates it when the other two get out of her sight, but then she just runs up and attacks the baby when they are together. Ungrateful witch!