In an alternate timeline where Earth became an ally of the Aschen, Samantha Carter stayed faithful to her decision to support the alien race until she discovered the sinister actions behind the scenes.
In the last ten years of her life, Carter eventually rose to the rank of Colonel before retiring from the Starfleet Marine Corps, married Joe Faxon, Earth's Ambassador to the Aschen, and worked on several major projects (one of which included the transformation of Jupiter into a sun).
When Carter and her husband were having difficulty conceiving a child, she along with Janet Fraiser began an investigation that led to the discovery of the Aschen's efforts to sterilize Earth's population through the anti-aging vaccine. The two women promptly told Typhuss James Halliwell, Daniel Jackson, and later, Jack O'Neill.
The group soon formed a plan to send a message through the Stargate and back in time ten years previous, warning their past selves to avoid the mission that would have brought them into contact with the Aschen. But finding that they needed a GDO to make the plan work, Carter confessed what she had discovered to Joe, who then revealed that he had known about the sterilization all along (although not to such an enormous extent). Nevertheless, he obtained the GDO for them, but gave it up only after O'Neill gave his word that Carter would have no further part in what they were planning.
Despite Joe's efforts, however, Carter turned away from her husband and rejoined her team in the plan's final execution. Even though the area around the Stargate was under heavy fire and O'Neill, Jackson, and Typhuss all lay dead around it, Carter ran to the Stargate to finish what they had begun. Picking up the message, she stumbled the last few feet to the Stargate and sent it through as she fell under the fire of the automated defense systems. (SG1: "2010")