Aside from Atlanna’s dalliance with Thomas, it’s unclear how exactly Aquaman will use Atlanna, though fingers crossed that she will swing a sword or trident at some point.
In the comics, Atlanna left Atlantis for the surface world, and while the circumstances of her departure depending on the DC Comics era, she is usually depicted as falling in love with the human Thomas Curry.
However, in the present day, Aquaman and Mera learned that she was actually transported to Pacifica, a magical realm for the Atlanteans who wanted to remain on land when the kingdom sank long ago.
In the New 52, Atlanna was forcibly taken back to Atlantis and was believed to have died while trying to flee Orvax, the military leader she was supposed to marry who was the reason she left Atlantis in this continuity.