Glad you got it figured!
I agreed with Skys post about it her "hiding from the bit". They can hide from the bit even if not rooting at the reins. If they pull the lips back off the teeth when gaping or chewing its a sure tell of stress. If she was stretching long and low there wouldn't be the mouth gaping and lips pulled up.
Again, glad it was a simple fix!
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.