Hello, Commonly backpain occurs due to disc or intervertebral disc problem. Other causes are ligaments and muscles stress, sprain or strain. She is advised to take acetaminophen or naproxen, one stat after food to get relieve from pain. Get her connected to a Physical therapist, exercises under observation and massage therapy are helpful. She can use pain relieving sprays (Volini). It is very effective. While having penetrative sex be gentle with her. Do it in positions in which she is comfortable. Get her clinically examined to rule out spine and slip disc problems. Get X-ray, CT or MRI done if needed. Get her examined by an Orthopedics or in the ER, she will be treated accordingly. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician