Warning! This post contains Black Widow.
Black Widow showed Natasha Romanoff’s deep cover family, but she never mentioned them to the Avengers before or after the events of the movie. Her past and her family have repeatedly been demonstrated to be a sensitive subject for her. Black Widow works to repair some of her relationship with her past, so why did it never come up before Black Widow’s death?
In Black Widow, Romanoff is shown to have been part of a deep cover operation in Ohio for three years as a child where she lived with a father-figure, Red Guardian, mother-figure, Melina, and a stand-in sister, Captain America: Civil War. The events of the movie bring the family back together and has Romanoff reconcile with them, accepting them as a family that raised her and influenced her life.
Despite forming closer relationships with several of the Avengers, particularly with Clint Barton and Bruce Banner, Romanoff never mentions this pseudo-foster-family. Prior to the events of Black Widow, this is because those memories are painful to her and she always plays her personal life close to her chest. While her connection with Avengers: Age of Ultron when she reveals to Banner that she was forcibly sterilized.
After the events of Black Widow, in Avengers: Endgame elsewhere in the universe, so is also out of communications range.
Finally, while Romanoff might have found someone to confide in during the five years before the time heist, it is likely that those memories were painful once again and her Black Widow family had been snapped. During that period Romanoff was working with everyone she could to keep control of situations–the absence of even Yelena, who she was closest to, suggests that they were not around at that point to be able to help. With Valentina Allegra de Fontaine sending Yelena after Barton in the Black Widow post-credits scene, this inability to share the news of her family is likely to cause some painful misunderstandings.
