My 7 year old often wakes up crying and sleep walking we have a very peaceful stable home what can be causing this she's also happy at school?

Somnambulism: There could be several other reasons causing this. Sleep study is mandatory. It will give you answers and direct you towards right management plan.

Sleep disorder: The spectrum of sleep walking, sleep talking and night terrors are relatively common in childhood.If the child doesn't immediately wake if you touch & try to console her she is in a deep sleep state, a night terror & not a nightmare.These are thought to represent reactions to sleep deficits. Improved sleep practices that add even a half hour/night can help.If not, consult with her pcp.