My daughter of age 8 wakes up in the night, and sometime walks, when said to go back to sleep, she sleeps back, what is the problem, how to address?

Walks during sleep: This is called sleep walking and is not uncommon among children. Talk to your doctor about getting a check up for your daughter.

Sleep disorder: Sleep walking/talking or night terrors all represent a sleep entry disorder. The emerge and worsen in those with poor or ineffective sleep, and improve when these improve. At 8, she should get no less than 9 hours sleep/24hr and more if physically active or studying.