Campbell7, overpronation is a tendency for "flat feet", where the longitudinal arches of the feet fail ( for various reasons ) to offer normal support. The forces that travel up the leg and thigh then tend to push the pelvis together somewhat, this has the effect of causing loss of sacroliliac joint movement ( a large pair of pelvic joints that are largely involved in buffering these forces ) and a stiff pelvis results. The Lumbar spine then becomes party to abnormal forces which contribute to the L3 problem I mentioned. In my own experience as a physiotherapist, all these issues are fixable within a two week time frame. Antipronation orthotic devices will re establish a normal arch posture and prevent abnormal forces . These are worn in the shoe as insoles, shaped to fit the person precisely. While it is possible to obtain these off the shelf , I recommend definitive devices made with skill.
I offer of course only general guidance and it must not be presumed that your daughter has or has not got a pair of "flat feet", or any other biomechanical disturbance without the guidance of a good physio.
Cheers