Although I don't have your and the many other friends who live in cold,snowy areas, I wouls suggest a excellent car cover with added old blankets etc for added cushioning with your idea of a solid wall that goes up to maybe 3/4 height to protect the car. I like your thinking of having the wall on rollers to aid moving around. I would park the car against the furthest wall away from the internal doorway and where Mother parks her vehicle and build a wall isolating the car from there.
We are enjoying a late start to our summer down here but I hope your winter isn't too bad or long.
Merry Christmas to you and your Family.