A muscle relaxant with pain killer will do in such situation. You would need prescription to get a medicine.

Well from the history you presented , it appears to be low back ache due to some compressive pathology which is radiating to the knees or it could be 2 separate problems presenting at once, would like to know about the pain in details and what occupation she’s involved in at present. Once the cause is understood she will definitely benefit from the medication , general pain killers won’t be of much help in her case

What is your age and profession it can be bad postural pain or spine disease pain consult me Dr Rajinder Sharma Senior Orthopaedic surgeon Chandigarh browse on goggle. Tks