So how, exactly, is Nat walking, talking and kicking butt in Black Widow? Don't worry, there aren't more time travel shenanigans at play here; ScarJo's first solo movie tells a story set at an earlier point in the sprawling continuity of the Marvel Cinematic Universe.
In the short teaser, Romanoff is revealed to be on the run, traveling under a series of assumed identities, which in itself is not so out of the ordinary given her history and employment as a super-spy. But in Black Widow, she's not just running from the bad guys: she's also eluding her onetime friend Tony Stark. Because Black Widow takes place during the superhero schism in between Captain America: Civil War and Avengers: Infinity War.
Fans will remember that Civil War ended with the Avengers splintering into two factions: those who sided with Iron Man and believed that "enhanced individuals" should sign the Sokovia Accords, and those who agreed with Captain America that they shouldn't be so quick to sign away their freedom. While Black Widow was originally Team Stark, she eventually helped Cap get away.
Romanoff went into "exile" following the events of that movie, and wasn't seen again until she returned alongside Cap in Avengers: Infinity War. Black Widow will explore how she spent those intervening months, including digging more into her past which was originally hinted at in Avengers: Age of Ultron, and introducing her other "family" aside from the Avengers, consisting of Yelena (Florence Pugh), Melina (Rachel Weisz) and Alexei (David Harbour).
It's also possible that a movie set in this time period could include cameos from other MCU characters who had not yet said their goodbyes, like Steve Rogers or Tony Stark. After all, what is a Marvel movie without a crowd-pleasing mid-sequence surprise appearance?