Avengers: Endgame hit theaters in April, and has since become the highest grossing movie of all time. The Russo Brothers made this happen by crafting a character-driven story that delivered countless cameos and surprising plot twists. But the narrative was also a bit complicated, especially regarding time travel, and the Time Heist to acquire the Infinity Stones. But with Endgame being released digitally and for physical copies, concerns and questions are being answered by the filmmakers.
One of the questions that has remained in the months since Endgame arrived in theaters is about Hawkeye and Black Widow's journey to Vormir for the Soul Stone. The idea is that Nebula knew what the price of the Stone was, and was therefore sending the pair of Avengers to their death. But the director/writer's commentary revealed the truth. As writer Stephen McFeely put it:
It should be noted, I've seen this on the Internet, that Nebula doesn't know about the exchange that's required at Vormir. No one knows other than anybody who was there. She just knows her sister didn't come back.
Well, that clears things up. Nebula has never actually been to Vormir, and doesn't know about Red Skull, and the Soul Stone's sacrifice. All she knows is that Gamora was taken there by her father, and the beloved Guardian perished in the process.
Nebula had a small role in Avengers: Infinity War, especially compared to Endgame. After being tortured by her father, she pops up in the epic battle on Titan. But she quickly puts the pieces together, realizing Thanos got the stone and Gamora was MIA. It's this realization that seems to make the fandom think that she knew what happened on Vormir. But according to the writers and directors, she did not.
Later in the digital copy's commentary Joe Russo also clarified Nebula's assessment of the Soul Stone, saying:
She knows her sister went there with her father and her sister didn't come back, and he left with the stone. So only assumptions can be made about what happens on that planet, but who knows? She could have tried to stop him and he murdered her. We have no idea.
This is another great point, and helps to show exactly where Thanos' emotionally damaged daughter's head was at while the Time Heist was being thought out. While she gave her limited intel about Vormir and the Soul Stone, she was in the dark about exactly how her sister died.
These comments strip Nebula from any guilt or association with Black Widow's heroic sacrifice on Vormir. Although one has to wonder: wouldn't Nebula want to travel to the planet during the Time Heist and find out what might have happened to her sister? It was in the past, so Red Skull wouldn't have knowledge of the actual events. But he would have revealed the sacrificial nature of the Soul Stone.