There is a possibility of nerve compression in lower back spinal cord level which might be causing this radicular pain. Is she also having any tingling numbness or difficulty in walking.
Next Steps
I will suggest you to start with hot fomentation lower back, analgesic with muscle relaxant tablet,
calcium and vit d supplement, analgesic ointment. she can also use lumbo sacral belt for support. If she doesnt feel better, she may require some investigations like X ray, MRI of lumbar spine..
Health Tips
Avoid heavy work, sitting down, avoid Indian toilet.