Turns out she is the best flier ever, falling asleep shortly after we buckled in and waking up only as we started to walk up the Jetway after the flight after landing in Chicago. As a precaution we did breastfeed her during the takeoff, to make sure that she could equalize the pressure, but during landing she was not even interested in a finger in her mouth, she was in such a deep sleep.
My only concern during a long flight with her would be de-hydration. Aircraft seems to have fairly dry air, and I think she may become dehydrated during the flight if she does not feed every few hours. Fortunately a flight to Chicago is still not too long at around 4 hours, however a trans-Atlantic flight may be a different story.