While this is a bit OT, I would encourage you to keep buying a ticket for your daughter now that she is over 2. The reality is that she is much safer when she is in her own seat.
As others have posted, I'm sure you could get away with declaring her a lap child for a while longer. I know I've see some kids who were quite verbal and potty trained as lap kids, more along the developmental lines of a 3+ year old...