I am hoping that it might be just a riboflavin deficiency, but I think Mareks could be a possibility with her walking when the hock gives out and she ends up walking on the hock. It is normal for them to help balance with their wings when they have a leg giving out. Only time will tell. Mareks has many different symptoms and can present differently in different birds. A leg can feel a little numb when they put weight in it. Their are similarities with Mareks and riboflavin deficiency, which mainly causes walking on hocks and curled under toes.
@rebrascora treats many birds with Mareks, so if she could have a look at he video in post 56, she would have more expertise. I suppose an injury to the hock tendon might also cause her hock to give out.