Mare at riding time

I rode today, with a french link bit on my mare. Bareback, she was good but after about twenty minutes or so she started acting up. She acting as if she doesn't want to ride anymore. In mid walk she stops, I try to turn her but she doesn't turn, she goes the other way. I try to get her into a trot but she won't trot.
What's wrong?

Is the bit hurting her? Are you just using your hands?

Is this a new bit for her? If not, I would say that has nothing to do with her problem.

It sounds like she needs work in the "my handler moves my feet" dept. Start from the ground-up...she should move her feet when you ask, NOW, backwards, forwards, left and right, without question.

Thanks everyone!
Yes the bit is new to her but I got off of her. The bridle was to loss, the bit could have came out of her mouth. That was the true problem, I just look at her and bridle..