I definitely understand that you might be tempted to give in just to make things easier. I've done that myself when my kids acted up in a place that wasn't conducive to normal discipline (Church, an important dinner or occasion, etc.).

Forewarned is forearmed. Your best bet will be to be prepared so that if you see that she is getting antsy, you can whip out something new to distract her. My daughter loved "Look and Find" books when she was a preschooler. They are very similar to the "Where's Waldo" books but can be found in kid friendly themes like Disney and Sesame Street characters. They require a good bit of concentration by the child so they can really be a lifesaver to make the time go by fast. You can work together and it's a very quiet activity. One book could keep a child occupied for well over a half hour.

My daughter also liked the magnetized dress up dolls. They come in a tin and I usually could only find them in airport gift shops. They were self-contained and easy to carry and kept her busy and quiet.

I'm always surprised to see Play-Doh and clay suggested. I know what a mess they make at home and I can only imagine what the seat areas would look like after a kid finishes playing with them on an aircraft. But maybe my kids were messier than most?

Books on tape are a great idea and we always used them on long car rides with great success as well.

Some of the Fruit Roll Ups snacks (Betty Crocker) come in shapes, games and patterns that might keep a child busy for a little while. Then she can eat them....(more of a distraction).

Whatever you bring, don't introduce it before the flight. New things hold attention much better.

And her phase is just your daughter asserting her independence. It's really a good thing. She's trying to be a 'big girl' and it can seem annoying to the parent, but it's the only way her little brain knows to get what she wants or to show you that she feels old enough to make a decision. It will end soon, and then start up again when she hits 13.