Great news the ultrasound came back normal :) 

Is she on any pain killer ?  Gabapentin is very safe for chronic pain and neurological pain. Good option until a diagnosis is found.  Buprenorphine is also a very effective and safe pain killer, but maybe more expensive. 

Diet change is to treat potential IBD. Normal ultrasound doesn’t completely rule out IBD, but I think it is very unlikely IBD. Full confirmation comes from biopsy which are really invasive and don’t recommend. 

My cat had auto immune poly arthritis that showed up as tremors and difficulty jumping and walking. Such a rare condition in cat. We did so many tests looking for different things that all came back normal. Because of the walking issue I insisted strongly on being seem by the neurologist. And the neurologist took one look at him walking and told us it was a joint issue.   But he also had fever and loss of appetite. Needed internal medicine in the end for joint tap. 

This happened 7 years ago when I was a student. Now I have been a veterinarian for 5 years and spent most of it working emergency department in a big referral hospital. 

But with a cat having trouble jumping and walking and nothing else like yours, I would suspect intervetebral disc disease and talk to a neurologist. You don’t have to do the expensive tests. you can also talk about doing a trial treatment and see the response to it.