Even if she does not have a paid seat you can always bring along your carseat. It does not incur baggage fees, and if there is room you may use it on an empty seat. If there are no empty seats, they can plane-side check it for free. Chances are she may feel more secure if she is strapped in AND you won't have to worry about a car seat when you arrive.
Also a new little toy or two can be a great distraction. Something that she hasn't seen in a while might work too. If you have a portable dvd player that could be a lifesaver. She is a bit young to be into TV but she might enjoy the sounds and colors of the Baby Einstein DVDs.
Snacks are also a good time waster, especially if you can make it into a game. I saw a snackbowl at the store yesterday with a plastic lid that requires you to push your hand through a hole to get to the cheerios or whatever. I can imagine that Austin would think that was a hoot and he isn't much older.
I'm sure you have thought of this, but possibly THE most important thing that you need to do for her is to have something for her to suck on during take off and especially landing. A pacifier, teething ring, or even a sippy cup will do, but you need something that will help her pop her ears.

I'll keep thinking. We have flown with one or both boys several times.