M.
We just got back from Florida ... actually we have been 4 times, starting when my son was 18 months old. I have a son, 6, and daughter, 2.
On the plane, here are the things I did: brought toys (I even gift wrapped a few small things for added distraction); lots of snacks, books, etc. We also went ahead and bought a seat for the kids when they were under two (even if they could ride for free), just to give some more room. We gave them decogestant, so the ears didn't hurt and to encourage sleep.
Also, we talked A LOT about it before hand. I went to the Disney website, read Disney books, talked about the plane ride, etc.
Remember, too, that you can stress for days and days, but it's only a few hours and then you are there. The hum of the airplane drowns out some of the noise and crying. And you will never see the other passengers again, so it's just not worth being too worried about.
The other thing - especially if you are worried about your daughter - is to be excited as possible. I think - on our first trip - my son totally picked up on my anxiety. She will look to you for cues, so I would be as happy as can be.
Once at Disney, I would recommend going at least one day in the evening. Less waits. Use the FastPass option. You might try and get in on a character breakfast or other meal - my kids loved it.
Like I said, we just got back and it wasn't very busy, but I think it heats up after Thanksgiving. In any event, the weather is PERFECT this time of year - it was 75-80 degrees, so the kids didn't get hot and cranky.
Also a stroller is a MUST.
Good luck - it will be fun.