Hi S.,
I think the biggest thing you can do is to buy her her own seat on the plane and let her sit in her car seat.
My husband and I flew with our little boy when he was 1 1/2 years old and it was SUCH a difference from when we flew with him at 5 months old (think nightmare-, versus dream-baby!!! :-).
By 1 1/2, he was soooo independent and no longer our cuddly baby that wanted to sit on our laps and be held all of the time (in fact, his favorite word while holding him was "down", repeated several hundred times, of course!!). So, our big mistake on that trip was bringing him on as a LAP baby!! (duh! it all seems so clear NOW!). Anyway, we vowed that the next time we traveled with him, he'd have his own seat!! Hopefully, you can benefit from our painful lesson...
Now, that being said, I would definitely bring snacks and drinks---the stronger the chewing or sucking that is required, the better---to help her ears pop!! We brought some low/no-sugar lollipops, along with some sippy cups, that required stronger suction, as well as carrots, that required stronger chewing or mashing, to really get the jaw working during both the ascent and descent.
We also brought some things to color, a few of his favorite toys/books, and some completely new toys / books that he'd never seen before---all to maximize the level of distraction.
And, definitely a change of clothes (or two) for any mishaps...
I hope this helps!
D.