We've traveled quite a bit over the years with our son (now nearly 5) starting when he was about 9 months old. My best tips for the little guys:
1. snacks - little ones and lots of them (like goldfish, teddy grahams, etc.) and give them one at a time to her.
2. photos of family, pets, etc. My DS spent at least a half an hour one flight giggling at a couple of photos of our dog.
3. stickers (as mentioned)
4. pipe cleaners - don't be afraid to look stupid (i.e. wearing pipe cleaner glasses or making pipe cleaner people dance!) Believe me, fellow travelers would rather see a silly parent than a screaming child.
5. more little snacks
6. if at all possible, get her a seat on the plane and take her carseat - it will be a familiar place for her and perhaps she'll fall asleep (always works for us).
7. some favorite soft activity toys - we had a little soft doghouse that had 3-4 little puppies that you'd put inside through various holes. That kept DS busy on a couple of flights.
8. some favorite books with lots of pictures - even magazines with big bold pictures to talk about.
9. did I mention snacks??? ;)
Have a great trip!