This, imo, is the most relevant part of the article, particularly since the child was well behaved on the flight down. Yes, sometimes kids scream on planes because they're brats with lousy parents, but, more often than not, the issue is ear-related.
I always bring a box of child-sized Ear-Planes when I fly just in case there are any kids on the flight who develop any problems. If you've got a kid with ear infection issues, they're a Godsend. And, for the record, I'll take a screaming child over some of the rude businesspeople I've sat next to any day of the week.
But apparently felt enough pain that she remembered that pain prior to takeoff? Wonder why she didn't scream on the way down?