If the disease were polymyositis or dermatomyositis the weakness would be pronounced and affect the proximal muscles. Those muscles around both the hip and shoulder girdles and it would most likely be symmetrical. It would not involve the type of sharp pain described.
As a lifelong athlete I have had numerous muscle, tendon and ligament injuries and some of them have had excruciating pain. A muscle tear is very painful and sometimes slow to heal. Most people do not realize that such an injury can often happen from a simple and normal movement. The injury does not have to be caused by something dramatic as you see in professional sports on TV.
If she is out of shape or over weight an injury can happen easily.
If the pain is localized then ice it down and rest.
Mixed connective tissue disease (systemic lupus, scleroderma, polymyositis), Raynauds phenomena, Hypertension, Barrett's esophagus.
Meds: prednisone 5mg, 50mg imuran, Lotrel 40/5mg, maxide 37.5/25mg, folic acid, potassium, aciphex 20mg, multi vitamins.
Maintain your optimism and you can beat the odds.
"Although the world is full of suffering, it is also full of the overcoming of it." Helen Keller