Hi. See the accident two months ago doesn't seem to have anything with her upper arm pain.
Patients with high bp and heart problems can have frozen shoulder.
Next Steps
Do find out if she has difficulty while raising her arm and while touching her back with that hand.
Health Tips
If she does have difficulty in doing the above activities, she may have Frozen Shoulder. I'm that case, she may need to apply a hot water bag twice a day, then apply any painkilling ointment, take mild painkillers and start shoulder exercises.