Hi -   There has been some good things suggested to check out in this thread, but I will add another possibility. I too have suffered from side/rib pain (both sides though) & nobody could figure it out either. At the end of October I had a laparoscopy surgery (where they go in and look around) for what I thought was an unrelated issue. Turns out I had severe adhesions due to endometriosis and my organs were basically "glued" together, and the adhesions were pulling on things. I realize that at your sisters age she probably doesn't have endometriosis, but it IS possible she has adhesions from her gallbladder surgery. Adhesions can form from scar tissue after having surgery, and can cause alot of pain.   I know how frustrating it can be with all of the Doctors, I have had my fill of that too!   Just something you may want to consider & good luck to you :)