There may be some soft tissue strain or ligament sprain around shoulder joint.. Sometimes there is a possibility of degenerative changes in the joint which may cause this problem..
Next Steps
She can start with hot fomentation, take analgesic with muscle relaxant, apply ointment locally, start physiotherapy. If not relieved, you can get x ray of shoulder joint to rule out any bony issue..
Health Tips
Avoid heavy work with left hand..