I'm trying to make the exact same decision. Do I fly with DD into Des Moines or Moline? One is cheaper flight with more expensive rental car and a six hour roundtrip drive, the other is quite a bit more expensive, but less travel time and no out-of-state car rental.
For me, your problem is much more cut and dry.
You couldn't pay me to fly into Chicago and then have to drive out. I would pay the extra money to fly into Indiana. Plus if you rent a car in Illinois, it will be more expensive if you're taking it into Indiana.
What college is she looking at?