We traveld to WDW last December, and wouldn't you know, the Tuesday before we left I found out that the stomach flu was going around my DS's classroom

! So, he went to school on Wednesday and then didn't go for the rest of the week!
We are big handwashers, hand sanitizers, wipe down with wipes, kinda people, so I just went a little nutzo with that. I also limited the playdates, which really wasn't all that hard.
LOVE the idea about wiping down the airplane seat - never thought of that!
Also, I've found that when I flip out

about sickness before a trip, my kids usually do not get ill - go figure. We were in Disney for eight days, and I packed Tylenol, Motrin, Dimetapp, those Sudafed plug in things, Vicks vapor rub, three brand new thermometers (I have three children, thought they each needed one!), and Pedialyte. I literally had a suitcase full of medication, diapers, wipes, and snacks! I also found every bit of information I could about the nearest hospitals and emergency care centers. My doctor wouldn't prescribe any medication when my kids weren't actually sick, so that was that. Well, NOBODY got sick on our trip, and I thank the no sickness fairy for that.

However, I got super sick once we got home and spent a week in the hospital, but that's a different story!
Try to have her get plenty of rest, eat lots of fruit and veggies, up the handwashing and have a great time!