I am so sorry for your friend's baby...Mybabe4me has a lot of experience with this, so she would definitely be a "go-to" person on this topic on how to rehabilitate your friend's baby.
Before I was married, I had a furbaby that all of a sudden lost feeling in his back legs in a matter of a few hours. Of course, we rushed him to the vet and they sent us over to the vet school. He was in extremely excrutiating pain, and he wouldn't let anyone touch him. He was hurting really bad, but he couldn't move his back legs. They told us he had a rare and inoperable case of myelomalacia which basically means deadening of the spine. Some cases are operable, some are not. This disease progressed extremely quickly, and by the time they were done with all the testing that day, he was paralyzed almost up to his neck...They told us our baby would never walk again and that this was one of the most painful diseases... He was in excruciating pain even with meds
They said it was congenital, so he was born with it, but that it just surfaced itself then...