Keep enough outside rein pressure, while playing with the inside hand. If she over bends, lift your hands strait up, and she should go straighter.
I would try the herm sprenger straightbar type bit
she's not in pain at all and her tack is perfectly fine as well as her health although she doesn't have the best confirmation
Assess for pain is the first stop. It sounds very like an avoiding technique. Get her back, teeth, and tack checked. Is it worse on one rein?