Buy some pee pads and try a trial run in a gas station bathroom.... the pee pads have a scent on them, which makes them want to pee on it.    
I haven't tried it in a plane yet, but Harley is grid trained (in the house) and he still uses the pads when we travel.    
At least with a trial run, you'll know whether she'll go on them.     
				__________________  Kendra  Harley, you were the light in my life, rest peacefully my love!       |