The story of her sort of finding her purpose and her heart again through this relationship with this kid, it just was really compelling. ... Over the course of the development of the screenplay, we probed more carefully and more deeply into the relationship of Danny and Mary, and really kind of committed to that as the emotional core of the movie. So that it's not only a thriller with action, and an exciting ride, but that there's also a genuine, real human relationship and real emotional experience at the core of the story. Folks who are interested in the action will certainly get what they want, but they'll get a lot more than they expected because there will be a very moving and emotional experience at the core.
Source : https://www.cinemablend.com/news/1738539/how-proud-mary-will-be-different-from-other-female-led-action-films