I'm the original poster and we have been home from our trip for a week.
On the plane, ME, and to the parks, I had her wear underwear with a pull up over her underwear. For sleeping and around the resort, she just wore underwear, like she does all day and night at home.
Pretty much every time we saw a bathroom, I asked DD if she had to go. I made her go in with me and try to go once an hour. Always had a proud, happy comment when she tried to go and actually went.
She did great the first 3 days, no accidents. 4th night, she had an accident while half asleep on the bus ride home back to the resort. Same thing the 5th night. I think she was just overtired, plus she had fallen asleep in the stroller and I didn't wake her for a potty break before getting in the bus, so my fault. Thank goodness she had a pull-up on over her panties or I would feel bad for the next bus rider! The 6th and last day was a mess, she had about 5 pee accidents, this was our last day and had already checked our luggage and we almost ran out of clothes bc it leaked out of the pull up!
Again, I think she was just over tired and over stimulated and overall did a great job.
The first couple days home, she had 1 accident a day, the last 2 days, no accidents, so we are back on track!
Side note: not to be gross, but we are talking potty training. She drank fluids all day long but somehow became constipated, maybe from the food or she needed more water (I don't know how, she seriously drank a ton of water and juice), or maybe was too excited at WDW to take the time for a "long" break. I had to call the ped and give her miralax, which thankfully I had brought. So just be aware that all systems can get out of whack when they are out of their routine.