Hope the vet check goes well

He looks like he needs a good physio to restructure the muscle wastage in the lumbar area of his back through being ridden hollow. He's probably stiff through this , and maybe 'bridle lame' (which is rider induced lameness rather than injury or conformational).

With time and flexion training to teach him to stretch into the contact, he's gonna be a stunner, and if he's strong for that rider its possibly due to the horse running away from the pressure of the bit..her hard hands making it worse.

I think you'll have a lot of fun bonding with him and retraining him to soften into the contact and round Love to see more pics of course when you get him :P