Background about the horse- Sassy is a 15 year old, 16hh Thoroughbred mare. When we first got her she had major trailering problems. Finally worked on that and got over that which was extremely bad. We always haul in a stock trailer and this was her only 4th time being loaded in a slant trailer.
So on Sunday we went to a horse show and we trailered with a friend, load/unloaded fine until we unloaded at home. My yearling filly was out in the pasture getting excited because she saw we were home and was whinnying. We had Sassy in the 2nd to the front slant out of a 4 horse and all the slants were stud dividers. I had tied the rope longer because she hates when it is tied short. I go move the divider and ask my friend to hold the divider against her and stand there so she wouldn't back up. So I'm just undoing the rope which was a slip knot, and she got excited and started backing up and my friend couldn't hold her back and had to let go. Sassy backed to the end of the length of the rope and when she felt the pressure she flipped out, pretty much acting like she had never been tied before. There was matts in there but with the horse poop/pee it was slippery, almost fell. I'm still up by the rope but she had pulled it so tight that I couldn't get it undone so I am holding the rope, and just talking quietly to her "hey, hey, settle down". She finally settles down and I get the rope undone and back her out. Then she acted like nothing happened.
She never does this in the stock trailer, and she can back out of the stock trailer fine. But in this trailer when her back foot went off she threw her head up and hit it. It never happens in the stock trailer which is shorter.
I can't really get someone to bring their slant trailer over to practice with, is there anything I can do and practice with in the stock trailer? We might be hauling up in that trailer again next weekend or the weekend after.
Luckily that night someone was coming out to massage her, and was there about 15 mins after it happened and she wasn't hurt at all.