Kate McCallister goes on an actual guilt-trip. Most people travel to France and experience the thrill of falling in love with someone with a sexy accent, the thrill of falling in love with a croissant with sexy chocolate filling, or the thrill of falling in love with café culture (so chic).
Kevin's ma? Not so much. She's just a nervous wreck.
Kate loves her son Kevin—she's just busy preparing their trip to France, and can't waste time listening to Kevin's complaints. After (understandably) ignoring Kevin's whining, her worst nightmare comes true: the family accidentally forgets about Kevin, leaving him home. Alone. This makes her feel like a bad mother.
On the plane to France, Kate's motherly instincts kick in and she senses that they're forgetting something—and finally, she realizes that something is Kevin. Freaking out, she tries to get in contact with Kevin…but the phone lines to their house were knocked down in the night. She calls the cops—who find her "hyper"—but they're not much help either.
Kate's feeling pretty guilty, at this point. Which, you know, makes sense…seeing as she left her eight-year-old son home alone.
While the rest of the family decides to wait for the next available flight, Kate trades off a watch, money, and jewelry to an elderly couple in exchange for their seats on a flight back the U.S.
This begs the question—why is Kevin's dad so laid back about this? Kate's trying to get back to Kevin as hard as she can, but dad is like, "Eh, we'll get there when we get there." Kate's strongly concerned about Kevin in a deeply maternal way: she wants to be reunited with her kid. Maybe Kevin's dad doesn't mind the idea of Kevin having to fend for himself a little bit? If so, they're playing right into some seriously outdated father and mother stereotypes.
Unfortunately, this flight doesn't take her straight to Chicago—it takes her first to Dallas, and then to Scranton, PA, where she flips out at the agent working at the counter when he tells her there are no available flights to Chicago.
Her speech reveals Kate's determination and desperation all at once:
KATE: This is Christmas! The season of perpetual hope! And I don't care if I have to get out on the runway and hitchhike! If it costs me everything I own, if I have to sell my soul to the devil himself, I am going to get home to my son.
Fortunately, Gus Polinski—polka bandleader extraordinaire—shows up, personifying the Christmas spirit. He offers Kate a ride to Chicago, since his band is headed back to their home in nearby Milwaukee. Of course, she accepts.
After some comic relief with Gus—whose story about accidentally leaving his son at a funeral home doesn't exactly put Kate at ease—she finally makes it back home, happily reuniting with Kevin. Ironically, the rest of the family pours in a moment later, having taken the flight that Kate didn't want to wait for.
So, that's Kate—loving, determined, and even desperate to get back to her son. She probably feels guilty too—but, as Gus would probably say, "Hey, these things happen."