Was this a doctor you spent much time with, in order that a skilled diagnosis could even be made, and who had the expertise to make that diagnosis? Does your mom not recall which personality disorder they supposedly said you have?

Because it sounds like it might just as easily have been something a doctor told her might be indicated, which without doing proper diagnostic work (which I'd think you'd recall if it happened) is all they really could have told her. Maybe you want to try looking the old doc up, if you can and if it's not going back too many years, to find out what if anything is on record. Outside of that I really wouldn't worry about it though, as your mom's offhand late retelling of this old info doesn't seem all that reliable. It's not that easy to accurately diagnose a 16-year old in the first place anyway (but very easy to misdiagnose); we're all pretty volatile at that point in life, with personalities still forming.