I see this thread was started years ago... almost five years ago to be exact. I have some info for the OP if they are still reading these. I am 99% sure your mother has slipped rib syndrome. It took me three years to figure out what my problem was (I didn't know it was related to my ribs - only my back pain, SI joint pain, and my TMJ in my jaw) - and then I discovered the slipping rib syndrome FB group, found Dr. Adam Hansen in WV, and flew to him this past April for a diagnosis to confirm what I suspected after lots and lots of research and taking to other folks in the group with similar symptoms. Unfortunately most doctors do not know about this and it does NOT show up on any standard imaging since it is typically a cartilage tear between your 9th and 10th ribs - which makes it very difficult to diagnose unless you see an expert in this field. Please look at Dr. Hansen's paper - and he can be easily reached for a diagnostic appointment. Just search his name and slipping rib syndrome on the web and you will find info on his minimally invasive surgical technique to tether your ribs back into place. I have my surgery scheduled for this November. Best of luck!