Thank you for your comment! First plane trip is exciting!! Although at 23 months, I hope she is napping, or you have a short flight and lots of friendly neighbors. Our son likes to walk around, and make new friends (saying "hi" to everyone on the plane)!
Her sitting on your lap with a stranger next to you might not be an ideal situation for a longer flight. Bring at least a couple of toys to keep her busy (and hide one for "emergency use" in case she gets bored with this first couple of toys!)
I hope you have a great trip!!