It's been a few hours and hopefully your daughter has resolved the situation, yet it's not uncommon for flight delays in the winter in Chicago. The snow/cold today isn't as bad as tomorrow is forecasted, yet I'd always advise to use a hotel app on your phone to make a reservation once you know you're not going out that night. There is a hotel connected to O'hare - the hotel website is
Hilton Chicago O'Hare Airport Hotel, and there are still rooms available tonight @ $239/night.
Good luck!