Character mistake: Inside the loop Barron said the only thing he can't change/shape shift is his eyes but when Emma and Enoch rush in Barron is able to change his whole body, including his eyes.
Other mistake: When the Hollow is approaching Miss Peregrine by the shore, it doesn't cast a shadow when it's invisible. But as seen several other times in the movie, Hollows cast shadows when they are invisible.
Chosen answer: At several points throughout the film, there are instances where her powers of air are used only as a plot device, so the extent of her powers is somewhat unknown. Therefore, it is possible she is able to make herself sit on the cart without floating, but other times isn't.
Amina Thommesen-Kähler