I've travelled a LOT with my girl, planes and automobiles, and you must pack some towels, napkins or baby wipes to clean up any messes (you can even grab some paper towels from the airport bathroom to have just in case!)
I always take a pee pad and we go in the handicap or family bathroom and try to make her go before we leave, or on layovers, but usually she is fine if she goes right outside the airport before we check in. I limit her water intake to the bare minimum while traveling and food, try to hold off feeding of feed earlier if you know its a factor on when they need to go #2.
Also, take a small blanket, baby blanket or big bulky coat and you may be able to hide her on your lap when you get up to a safe/ flying range. They have to be under the seat for take off and landing, some flight attendants are cool about letting them sleep in your lap, others are kinda bitchy about it, but you don't find out til' you get caught..lol and I have only gotten caught a few times out of the many I've taken her, I usually just pull the blanket over her when they walk by and watch my iPad or read a book.
Take off and landing are the scariest to them because of the noise and air pressure changes, but she should be fine unless someone in the seat in front of you has ordered fried chicken and the smell of it is making them go berserk!! *sigh* lol
Have a nice trip! If you use bells on the door for potty, bring them, they will figure out how to use them at new places quickly. I don't bring ours anymore because Gucci has figured out to go stand at the door of whatever hotel room or house we are at. We just got back from a 2 night stay in Blacksburg, VA for my DD's graduation, she's happy to be home, but she loves traveling with us! and we love taking her