I'm sorry - I hope this is something you and she can deal with, and that she responds well to the meds.
I had a kitty several years ago that had a similar issue. With him, we woke up one morning when he was about 6 months old to find he could not walk with his back legs anymore. The day before he had been hiding some, but we thought it was because it was Halloween and the doorbell kept ringing. Prior to that, we had no indication of anything wrong.
It wasn't quite the same problem - with him, a bone in his spinal column had started growing abnormally and compressed his spinal cord. It was the bone under the spinal cord that had the problem, and they couldn't do anything with it. They ended up doing surgery and removing the bone on top of the spinal cord so the cord wasn't compressed at least. When we decided to do the surgery, they told us it was about a 50/50 chance. I thought they meant of him walking again. If I'd realized they meant a 50% chance of even making it through the surgery and that they really didn't think he would ever walk again, I don't think we would have done the surgery.
It turned out reasonably well, though. They didn't tell us anything to do with him to help him - mentioned that there were carts for animals that had walking issues. So I devised my own "therapy" for him. Once he recovered enough to start trying to move around, I started trying to help him learn to walk again. Several times a day, I would put a towel under his stomach and use it to hold him up while I walked around with him.
He never walked the same again, and when he ran, he actually hopped like a bunny. But he got around reasonably well, and even climbed the 5 foot tall scratching post all the time. He did have seizures the rest of his life - probably from damage to his spinal cord. He lived until he was about 8 ½. He finally started having problems walking again, to the point where he couldn't even stand enough to use the litter box. I had to have him put to sleep at that point - you could see it in his eyes that he was miserable.
Sorry that was kind of long.... the point is, even once he was walking again, he fell over a lot. It made it difficult for him to use the litter box - he would frequently fall over while in there, and then the litter would stick to him and make a mess, I'd have to give him a bath, and that was really a pain with his leg issues.
So.. the part that might help you.... I basically designed him a special litter box. It was narrow - just wide enough for him to walk into. It had high sides, and was basically open on each end. the ends each had just a small edge (maybe 2 inches or so) that were just tall enough to hold in a small amount of litter, but short enough that he could step over them without any issues. That way, he walked in from one end, the tall sides would hold him up while he used the box, and he just walked straight out the other side without having to turn around. If I remember correctly, we used a cheap shoe shelf from Walmart and just modified it to make the box.
If she is doing ok, but starts having problems in the litter box, you might consider doing something like that to help her. It helped my Sebastian a lot - without it, I don't know if we could have dealt with the problems of using the litterbox. We even considered just lining a box with puppy pee pads at first, but it didn't keep him from making a mess of himself. The litterbox I designed did for the most part.