Well, I got 27 years of living in the Chicago burbs, so here goes;
Clear day - Take her to Sears Tower for a good vista.
Nightime - Go to the 95th floor in the John Hancock Building
Daytime - Walk along North Michigan Ave., let her see the stores, or walk the lake front Shedd Aquarium to Navy Pier.
Museums - Science and Industry, Shedd, Art Institute.
Hotels - well there isn't any cheap hotels downtown- find a chain like Holiday Inn, or stay in the burbs outside of Chicago
Places to listen to the Blues - Buddy Guy's Legends, Kingston Mines, House of Blues, Back Door, lots of good places, etc.(Fitzgerald's in Berwyn is great), and if you dig the girl your with, take her to the Redhead Piano bar - seating around the piano.
Movies - 900 N. Michigan Ave.
Hungry? So many places to eat...Seafood is Shaw's Crab House(I'm from Maryland, I know crabs), Signature Room 95th floor of John Hancock Building, deep dish pizza(you don't get bad pizza anywhere in the Chicago area, best thing Wisconsin ever did was CHEESE), Houston's, Ed Debevic's, Pick em'
Chicago is a great city...but like any city, it can bite you, don't venture away from the downtown when on foot, stay around the Loop, North Michigan area, Navy Pier, River North, and Near North areas. Be aware of who is around you, and where you are...
Thorns
P.S. If you see the Old Onz Oldman, he knows Chicago better than Richie Daley