My 85 Year Old Aunt Complained Of Pain And Very

My 85 year old aunt complained of pain and very limited movement in her upper right arm/shoulder area for over a month. Then on 1/1 she woke up and her arm - from elbow to shoulder - was completely black and blue (deep bright purple). AND, no more pain and limited movement.

She went to her doctor who was stumped. He sent her to therapy for the arm, but they said she had complete range of use and didnt need it.

Any thoughts what may have happened?

I should tell you she is on plavix.