What Causes Recurring Pain In Upper Arm While Having Diabetes?

hi. my mom has been complaining of intermittent right upper arm pain for the past several weeks, she's complaining about it now. she describes the pain as sharp and throbbing. she's 76 y.o. with heart disease history and diabetic. she denies any dizziness or nausea. she's going to call her doc in the am. i know this could have many causes, but any ideas? thanks...