Answer to Question 1
Osteoarthritis is a wear-and-tear disease seen usually in the elderly. Rheumatoid arthritis is an autoimmune disease in which the body's immune system attacks synovial joints, triggered by an infection or some other cause.
Answer to Question 2
Her pain is probably caused by injury to the rotator cuff, which can result from repetitive motion, trauma, or excessive force. The rotator cuff consists of the tendons of four muscles that stabilize the shoulder joint. If torn, surgical repair may be indicated.