There is absolutely nothing new about artists being refused entry or forced to cancel gigs in various countries. She's not the first and certainly won't be the last.
Seems to me the Beatles had to rent a house on the Canadian/American border just to sit in the same room and that was long before Sep 11.
Not knowing is not an excuse.
Musicians Unions are pretty good at keeping the paperwork straight for international gigs. About all they are good for really.
Or you could get yourself a manager........