As Scarlett Johansson told Entertainment Tonight, something that is rich on a character level is what excites her most about a potential Black Widow film, and part of what would compel her to do such a project.
She is now a fugitive because of the choices she made in Captain America: Civil War and that growth could continue in a solo film.
As an Avenger, Black Widow is a vital part of the decision making process and she has begun to do what she thinks is right, regardless of legality or allegiance.
At each of those points, she was a subordinate, sometimes operating independently, but always on someone else’s orders.