My mare (whom I had owned for 6 years at the time) was such a fussbudget when I moved her to my most recent barn a couple of years ago. As I said, I had owned and ridden her for 6 years, she had been moved several times before without problems, but this time around, she was a little jerk. I think it was related to the fact that due to personal reasons, I had not worked with her much in the months right before that move. My barn owners have always told me she is much better behaved when I come out regularly anyway.
Anyways, she eventually got over it and settled in. Had I not known her I would have been really worried because she acted up for a good two weeks. I knew my good girl was in there somewhere. I just went out and handled her every day I could. I even did some positive imagery when I was driving over to the barn. I find if I expect things to go well, they often do.
I think this mare has just had her world turned upside down and is reacting. Cannot blame her. And she will probably test the new owner. Just keep having her owner handle her consistently. If she is not safe to ride yet, just groom and take for walks. If not safe to walk yet, just groom. Baby steps, she will get there. Celebrate small improvments, not every horse reacts the same to major change. She needs time and consistency to get used to her new surroundings, and to bond with her new human.