Two years of worsening symptoms, no diagnosis

* female, 84, 5', \~160lbs, white, non drinker, previous smoker (quit over 30 years ago) * history of a brain tumor successfully removed in her 20s, stage 1 bladder cancer successfully treated in her 60s, hip replacement \~15 years ago in which a tendon was nicked resulting in sustained discomfort and walking with a cane, wet age-related macular degeneration * current unresolved symptoms * poor balance * frozen gait * some urinary incontinence Prior to the current symptoms, my mom had been in good health. However, over the past few years, her balance has essentially become nonexistent. She cannot walk at all now without assistance and fallen several times in the past 2 months. She has been to neurologists, physiatrists, and physical therapy with no answers or improvement. The latest hope was a normal pressure hydrocephalus diagnosis, but a CSF test came back clear. There is no cognitive decline. What could this be??