She’s standing next to Michael B. Jordan, who will be playing Erik Killmonger in Black Panther, so it would seem that the pair will be working together, or perhaps Nightshade is working for Killmonger.
In the comics Tilda Johnson has gone by several slightly different monikers, from Dr. Nightshade to Deadly Nightshade, to simply Nightshade.
Since then, the character has been an antagonist for the likes of Luke Cage and Black Panther.
Based on this single image, we’d guess that Nightshade will be Erik Killmonger’s right-hand, that is where she’s standing after all.