What can cause sciatic nerve pain in a 16 year female?

See details: Congenital spinal stenosis, disc herniation, abdominal issues such as endometriosis and local trauma are possible causes. An MRI of back would be helpful.

Many causes: Sciatica in a young female has many potential causes, such as Pyriformis Syndrome. In my experience a common cause is impingement of the pelvis presacral plexus, which is the "headwaters" region of the sciatic nerve. Subluxation of the sacroiliac joint due to ligament laxity can evoke exaggerated movement of this joint, which is contiguous to the plexus. See an Osteopath for an evaluation.