We just went to Savannah last summer, and it is a lovely town. You've already received some excellent advice: you must eat at Lady & Sons and go on a ghost tour (some are walking tours, others are horse-drawn carriages, and one is in a hearse!). Other ideas:
Go out to Tybee Island, but skip the Marine Science Center unless you want to pay $6 each to see a dozen aquariums of fish. Seriously, we did a nature program, which was wonderful, but just going in to see the facility would be a total waste. Tybee Island is an old-fashioned type beach with a big pavillion (cheap food) and lots of little shops. You can take a dolphin cruise or climb the lighthouse.
We ate at the Pirate House, which is supposed to be (or rather, to contain) the oldest building in Georgia. It was good, but it can't hold a candle to Lady & Sons.
Shop at City Walk.
See portions of the Underground Railroad. I forget the name of the church, but we stayed at the Doubletree (I think it's about to become a Hilton) at 35 Bay Street, and the church backs up to the hotel.
Take a tour of historic homes. Don't skip the cemetary; the Union soldiers changed lots of the tombstones, so that people died before they were born, etc.
If you think your daughter isn't ready for a ghost tour, try the Pirate Tour. I haven't done it myself, but it looks good.
When you get to town, go to the Visitor's Center for lots of tourist brochures and coupons.