Hi Thank you for asking HCM. I have gone through your query. Your daughters problem can be due to strain of ligaments and pressure on tail bone area due to over stretching. it is better to go for a local examination by an orthopedician and an X ray if needed. Ice pack application locally, taking over the counter NSAID like ibuprofen and avoiding constipation by taking stool softeners will be helpful to relieve the pain. Violent physical activity should be avoided till recovery. Using a supporting doughnut pillow while sitting will be good also. If no improvement then local injection of corticosteroids will be helpful. Hope this may help you. Let me know if anything not clear. Thanks.