Seems to be some type of attention seeking strategy where she is running to the Dr. to be checked out or enacting situations or illnesses that are actually happening to people in her surroundings. To me it reads as though she knows there is something wrong but she can't work out what it is so the behaviours she brings out may in fact be some form of cry for help by someone who cannot express themselves so it's just easier to copy others and lie. You mention it's become worse since her twin was diagnosed and that she doesn't seem to care if she is caught in a lie. This may well be because she is looking to someone else to take control over a situation she has no control over within herself. Let alone understands. Nobody wants to confront her over her lying. To me it reads as though there is no need for confrontation about her lying as that will achieve nothing, but perhaps it is well overdue that she is gently guided to a mental health professional.