If her time is linked at the aquarium, tell her to go see the whale sharks first. They are something I haven’t seen at any other aquarium.
There are penguins at this aquarium. Very unique.
Another vote for the CNN tour.
CNN tour is awesome, so is the aquarium. If she’s a college football fan, the College Football Hall of fame is actually pretty interesting (and I’m not a big fan like the folks I went there with!). These are all walking distance I believe.
World of Coke is good too. FYI the way the aquarium is set up, you can choose which exhibits to see first if she has limited time. Of course, you still pay full fare 
Sorry the weather is so crummy! We haven’t had a full week of rain like this in a very long time.
She does like football - though prefers NFL even though she lives in the city where those “Buckeyes” reside! I don’t know if she is aware of the Hall of Fame - I’ll share that!
Make sure she leaves plenty of time to go through security at Hartfields. DH flew out last week and this week for business and he said it’s seems like it’s taking longer to get though.
@abasket, please tell your D that Atlanta isn’t always this horrid…she is officially invited to come back and hang out in Piedmont Park (inspired by Central Park in NYC), Stone Mountain Park (largest granite outcropping in the world), nearby lakes, museums, theatre, ballet, etc. We even have IKEA ! So much to see and do, and a variety to please just about everyone.
The joke around here is if you don’t like the weather, just wait a few hours and it will change. We add a sweater to wait at the bus stop in the early hours, then take sweater off before noon. Change into shorts after work, and then maybe pull up the extra layer of covers to go to sleep. Our more normal weather is to have rough thunderstorms and then they are done in just a couple hours. We just don’t know how to handle a full week of continuous rain…