She was turned out for the 2nd time with a new boarder, an absolutely gigantic draft cross mare. I went out to the field to get Izzy as I always do; she and the new mare were out on the grass, but when they heard the gate, they charged and came galloping across the field towards the gate. No problem, I figured once they got up to the gate, they'd stop and I could just grab Izzy. Well, as I approached her, she pinned her ears and spun around, as if to kick me. I thought, "not acceptable," and swung the leadrope around to drive her away from the hay that was on the ground near the gate and back out onto the field, thinking that a) she didn't get to try to dominate me around the hay and b) it would be easier to get her when she and the new mare weren't both jockeying for position over the hay (it was in multiple piles, and they were driving each other off going from pile to pile).
But as I approached Izzy in the field, she again pinned her ears and threatened to kick. Then she and the new mare turned and stampeded back towards the gate. I approached Izzy again, and same thing. At that point, I felt like it was getting a little dangerous as she and the new mare were also snorting at each other, and I didn't really want to be in the middle of it, so I left her out there and wasn't able to bring her in to ride.
At any rate, I've never had trouble catching her in the field, regardless of who she's turned out with, and I felt uncomfortable because she was acting so aggressive. Obviously, I'm worried that she'll now think all she has to do is make a fuss and she won't be ridden. I didn't feel that it was an option to tie up or take out the new boarder because she's not mine, but it's likely that they'll continue to be turned out together, so I need to solve this.
I will definitely be talking to the BM when I go out to ride tomorrow, but I'm curious to hear what others would have done in this situation to make it less dangerous and successfully catch the horse.