WARNING: The following contains minor spoilers for The Falcon and the Winter Soldier Episode 3, "Power Broker," now streaming on Disney+.
Sharon Carter made her return to the Marvel Cinematic Universe in the third episode of The Falcon and the Winter Soldier, and it was a dark return for the former S.H.I.E.L.D. agent and legacy hero. Falcon and Bucky learned that Sharon never received the pardon they did after Captain America: Civil War. She now lives abroad in Madripoor, a lawless safe haven, where she built a life for herself outside of the law. While this was a shock for the MCU, it's far from the most questionable thing she's ever done in the comic book Marvel Universe.
In the Marvel Universe, Civil War ended with Captain America surrendering when he realized that the war between superheroes was tearing his country apart. In 2007's Captain America #25 by Ed Brubaker, Steve Epting, Frank D'Armata, and VC's Joe Caramagna, Captain America prepared to stand trial for his perceived crimes. He walked up the courthouse steps, and an unknown assailant shot and seemingly killed the legendary hero. Falcon and Winter Soldier went after who they believed to be the shooter, Crossbones. While they were battling Crossbones, the person who really assassinated Captain America, Sharon Carter, sat by his side.
However, a couple of things about the attack exonerated Sharon of wrongdoing in the death of Captain America. The biggest of these is the fact that she was brainwashed and mind-controlled by Red Skull. As the crowd scattered after Crossbones' gunshot, Red Skull and Doctor Faustus released a command in Sharon's subconscious and forced her to shoot Steve Rogers point-blank on the court steps. What was worse for Sharon is that she could remember this moment and had no idea what to do next. When Sharon learned she was pregnant, Red Skull knew as well and planned to use her child for his own devious plans, adding a level of horror to an already terrible situation.
Things got out of control with Winter Soldier taking Cap's shield and Sharon Carter quitting S.H.I.E.L.D. and trying to help Falcon track down Bucky. In Aleksandar Lukin's body, Red Skull brought in Arnim Zola, Sin, and Crossbones to help, and in the ensuing battles, Sharon lost her baby. However, Sharon began to have nightmares and believed that Steve might not be dead after all. In the end, she was right. In the 2009 Captain America: Reborn miniseries by Ed Brubaker, Bryan Hitch, and Butch Guice, it turned out the gun Sharon used wasn't a real gun. Instead of dying, Captain America was locked in a fixed point in time and space and relived the biggest moments of his life, as the full extent of what had transpired came to light.
Eventually, Red Skull pulled Steve out of time and took over his body, which was his plan all along. However, Rogers was also in the body, and he fought back, defeating the Red Skull and returning to the land of the living. At this time, Steve chose not to continue fighting as Captain America, allowed Bucky to continue in the role, and then took on a new duty as Steve Rogers.
Rogers then formed the Secret Avengers, and Sharon Carter was one of the first people he brought onto the team, proving that he had faith in her and never blamed her for his assassination at all, Instead, he credited her for saving his life and helping him return from the dead. In the end, the two rekindled their romantic relationship and continued on as a couple, proving that not even death can really keep a good hero down.