I love the Palmer House and even if you don't stay there, be sure to go see the lobby. It's special. You might also consider taking her for high tea there if she's into that sort of thing. Do consider getting a room on the club level if you can spring it; the dedicated elevators are nice and the breakfasts in particular are solid.
I also had a very good experience at the Westin River North, but for ambience/style it can't hold a candle to the P-H.