Hi
Welcome to the MedHelp forum!
What your daughter has could be spina bifida or pilonidal sinus. In spina bifida the lower end of the spine does not close. Pilonidal cyst and sinus are almost the same. A sinus is always there and if its outer mouth is open, it keeps draining fluid. If the outer mouth is closed, then a cyst forms. Both begin with a hair invading the skin layers through a dilated hair follicle, thus forming a sinus tract.
Since I cannot examine your daughter I have listed the various possibilities that should be looked into. Please consult her pediatrician for examination to clinch a diagnosis. Take care!