Reins not reigns. And cues not ques.
Have you checked saddle fit and placement? And have her teeth been done? It could be when your weight is in saddle that it is hurting her.
Could also be that your saddle has something wrong with it, loose nail inside it that is poking out? Or even broken tree.
You also may not be still with your hands and seat, aggravating her. Or bit might be irritating her too.
There could also be skeletal problems that show up mainly when under saddle.
Too many variables here.
And when she is doing this where are you at? Paddock or pen, or out in pasture? Just because a horse will stop well at liberty, does not mean it will under saddle.
You need, once saddle/vet issues are checked out, to work with her in smaller area if you are in pasture, making sure the basics of being ridden are solid.
Horses make me a better person.