In the video it did appear that she was sitting on her hocks or elbows. I really hope it is just a riboflavin deficiency or a sprain. The sooner riboflavin deficiency is treated the more chances of recovery, but in longstanding cases it does not respond well. Mareks vaccines are not 100% successful, so watch her for any new signs, such as a paralysed leg or graying of the eyes or changes in the pupil shape.