At that age we brought the car seat, put ds in it, and he usually slept for at least an hour, if not longer. Maybe you'll get luck and she'll get bored and take a nap.
We also brought coloring book, but I recommend
triangular crayons for the plane. They don't roll, which is just terrific.
Always bring your own snack food because for one, airplane food is blech! and besides the food/drink cart is never coming down the aisle when you need it. I also recommend buying at least one bottle of water after security to take on the plane (they never give enough and airplane air is dry and will dehydrate one faster than usual). A child that is not hungry will be happier and also more likely to sleep.
Bring small, non-noisy toys that your dd hasn't seen before, or if you don't want to buy a bunch of new toys, then take some out of her current stockpile and put them away for a few weeks before the trip so they "seem" new.
Oh, nothing that rolls, and only give her one toy at a time!
Finger Puppets was one idea I read, if you're good at making up stories.
I always brought a couple of small board books. The lift a flap books were usually a hit and would keep ds entertained a little bit longer.
I think the color wonders are great especially for this age, and the sticker books might be a great idea too. Anything sticky, even a roll of regular scotch tape, would probably be fun for achild to play with. You just want something that isn't hard to remove before the end of the flight.
hth!
