Your friend needs to go back to her GP and insist on them looking at her shin again. She must not worry about bothering the doctors - it's their job after all and what they paid for !!
I once had a really sore foot, could barely walk on it, went to Casualty, had it x-rayed and they discovered I'd broken a little bone. It must have happened some months previously from the healing that had taken place but I'd put up with the pain because I didn't want to bother the doctors !!! Daft or what ?