An odd thing that I have seen with the dwarfs that may account for her behavior is that in shipping, they all try to hitch to the smaller ones. I started only shipping same size horses or shipping in seperate bags in the same box.
Way too many times, by the time I was through bagging and was starting to box, the bigger ponies would be hitched to the smaller ones even when they had grass in the bags to hitch to.
I bet they hitched on her through the shipping, if that's the case, she will take a little more time but will be fine.
This may not be the case but thought I would mention it as it seems to be normal behavior for them and when you mentioned that she was the smaller one.......