The Asgardian warrior woman Sif from the "Thor" movies will be in episode 15. That should work out to be broadcast on February 18th.
UPDATE: It's going to be on the Toob March 11th. (That's tonight, Tele-Folks!)
ABC Entertainment Group president Paul Lee said:
"We're shooting it now. Jaimie Alexander [who plays Sif] is there. That's going to be absolutely integral to that hour of television."
And this is from the Marvel website:
"Sif has come to Earth with a very specific mission. Unfortunately, we can’t tell you just what brings her to our neck of the woods just yet."
|Sif in "Agents Of SHIELD"|