Hi
If all the Cx treatments fail, I suggest looking at the deltoid bursa which may cause impingements, plus the supraspinatus tendon area. Does not sound like scans have been undertaken to confirm any pathology. Try a reputable ultrasound scan, plus possible CT or Wikipedia reference-linkMRI if symptoms remain unresolved.

Prior to scanning, try deep pressure at a 45 degree angle to the acromion, over the supraspinatus tendon, plus deep friction over the teres muscle insertions. Strengthen the shoulder depressors and retractors. Does the patient have a problem laying on the affected side, and is night pain a problem. Any impingement on shoulder abduction?
Regards
MrPhysio