TV Insider reports Jaimie Alexander will reprise as Sif in episode 12, which will see Sif come to Earth on an undercover mission where she encounters a villain with superpowers that are equal to her own. The ensuing battle is said to take place off the coast of Portugal and becomes big news. The fight tops social media causing the SHIELD agents to rush in and investigate only to find Sif without her armor and suffering from short-term memory loss.
"Sif has no idea who Thor is or that she serves a king, and we're going to have fun with that," executive producer Jeffrey Bell said. "It'll give us some much-needed humor in a season that's been full of betrayal and death. Sif can't even recall who she came here from Asgard to stop, but Agent Coulson [Clark Gregg] and his team will try to help her figure all that out."
It is said Sif hasn't forgotten everything as she does know she is an alien and from Asgard.
"We've been dealing a lot with space aliens and Inhumans in our last few episodes—things our Earth-bound heroes just don't know much about," Bell says. "They need help understanding what's really going on. Sif's memory—what's left of it—will come in very handy."
Marvel's Agents Of S.H.IE.L.D. returns March 3rd; the Jaimie Alexander Sif episode airs March 10th.