Do you ride in an arena? Does she do this behavior in a certain spot in the arena, next to the gate or in one corner? My sister had a gelding who would do the stopping, bucking behavior at just one end of the arena. As long as you avoided that bottom third, he was fine, a dream to ride. If by some miracle you got in that third, hijinks ensued. Not sure what it was, shadows or maybe a bad memory of the end of the arena.
Does the behavior coincide with her hormones? My mare sometimes does this same behavior the week before she goes into heat. We don’t have an arena, so I hack around our three acre yard. She will drag me up to the barnyard and stand there and ignore my kicks, clicks, kisses, reins in both directions. She simply turns her head and looks at me. I will sit there for awhile and sometimes she gets upset that I don’t get off and let her have her way. I can tell she is annoyed because she stomps her hind right. This is when I get off her, lead her to the other side of the yard, get back on and keep her working in small-medium circles away from the barn.
You mention she resists the right rein. I would second the motion to have her teeth looked at and get her vetted, but also try some massage or stretching techniques on her poll and neck. There is an article in the latest Practical Horseman (or Equus. I have a stack of magazines and read them all in one sitting.) about it. I have done some of the stretches with my gelding and he has become much more willing to move.