Hi. My daughter is 7, has ADHD. Thyroid hormone resistance, and was treAted for Lyme s a year ago. For about 2 months her teacher and 2 different substitutes have noticed that when she has been sitting she is physically unable to get back up without help. And once someone does help her then it takes a few seconds for her legs to relax and unbend or uncross. They said it is more than just her legs falling asleep. It happens about 1-5 times a day
Your daughter needs to see a Neurologist on an urgent basis.  She could be exhibiting symptoms of a chronic infection of the central nervous system, seizures, damage from an earlier medical problem, a lesion in the spinal cord, problems with blood flow to the brain or any of a number of other reasons for these serious observations.