If the end and start point is the same, the routing and class unchanged, and there hasn't been a change to taxes (etc) then she may well be correct. I would, however, check in at the first possible moment (which is 48 hours in the case of Cathay). So typically being moved on the same day does not need reticketing, merely revalidation. If you booked a long, long time ago and say a new tax has been introduced, or perhaps a really big exchange rate change, then it may still need re-ticketing, but there would be a natural bias not to do that if possible.