I’d like to bring a designated driver to the cocktail event. Can I bring her if she’s not 21?

What the other answers state is correct. Here is a link directly to their events page. https://atlantabg.org/visit/events/cocktails-in-the-garden

Yes you will be completely fine. You can approach drink tents too, if she isnt getting anything at them it is not an issue.

You should be fine - inwould arrive around 5pm since the event will occur within thebgarden. She should be free to walk around, just dont approach the drink tents