Do get her checked out for physical ailments but also be aware of where she is settling in the herd order. Many times if she is low horse on the pony pole, she will try to dominate her human.
My lowest horse is the one I have to be more dominant with or she will walk all over me. She tries all the things you stated your mare is doing. Some mares also have a hard time with their monthly cycle. That should only last a week or 2 at most though.
Good luck in getting it sorted out.