My 15 Y O Daughter Has Been Complaining Of Pain

My 15 y o daughter has been complaining of pain with sitting at, what appears to be, the coccyx bone area. She doesn't remember falling or injuring it. She runs track and long jumps but this does not seem to bother it. Sitting in a wooden chair at school does.
What do you suggest as the first course of exploration? xray or MRI