I am so glad the chiro worked on her already as she is very lame and sore on the right in the video
Your MIL is right - no riding until the mare walks sound at liberty. As sore as she looks to be, she may even need another chiro treatment in 4 weeks since the Atlas bone and/or Poll were involved along with the shoulder.
Regarding hay. It is an established fact that a horse should eat 1.5% - 2% of their DESIRED body weight in forage daily. I feed 2% of the desired weight and there is always hay left in the bag the next morning
I have two metabolic TWH's. I also have a scale in the barn, weigh their hay, and give it to them in a slow feed hay net.
They are on pasture during the day, in at night; one wears a grazing muzzle, the other doesn't need one because his issues are more endocrine related than insulin.
Meaning, buy her a Tough-1 grazing muzzle from Chicks. They have huge nostril holes for these big-headed horses. Cursor below the muzzle and there sits the slow feed hay net for $8 Saddles Tack Horse Supplies - ChickSaddlery.com Tough-1 Easy Breathe Grazing Muzzle
I apologize, I didn't even bother to look at how you ride - lol lol All I saw was a very sore horse.
Please listen to your MIL and stay off her until she is sound. The best exercise the horse can get is self-exercise until she stops favoring that shoulder. She will move herself in a way that is comfortable to her. If she is by herself and refuses to move, then scatter some hay piles around a paddock and force her to walk that way
She is a very pretty gal, good luck with her