Stress fracture and disc protrusion

My daughter is ten years old with a past history of sensory integration problems along with hypotonia. Recently she presented with leg pain, and was sent for a MRI. I am shocked and confused at the findings. She has a stress fracture of the second sacral segment, in addition she also has Disc protrusion with thecal sac impingement from L2-3 through L-5-S1 level. She has suffered no injury, nor fall. She was fine one day then complained of leg pain only while running the next. Due to her sensory problem I always know that when she complains of pain to get it checked out. Even with the reports coming in she still experiences no pain, unless she is trying to run, which we were instructed not to do. I understand what all this is, but do not understand how a ten year old presents with such problems out of no where. Any help would be greatly appreciated.