Personally, I've experienced a herniated lower-spine disk that resulted in much the same symptoms, ultimately not being able to walk other than short painful steps. Took 3 weeks bed rest and 6 weeks of therapy just to walk with a limp and then over a year to get rid of the limp...
Also experienced something similar with our small Jack Russell terrier-mix that on getting out for the first time to play a couple of years ago overexerted herself and hurt her spine, almost crippled herself - both legs would not work for several weeks.
Vet recommended getting one of those snap-on pet flotation devices and having her float in a warm water tub to exercise those legs as she was able to. She still does not have right full hind leg functionality/movement - she just kind of drags it along. Unfortunately, given a chance she'll run a cat on three-legs as fast as she can go.
Hope it works out for both of you.