Sif was recently sidelined in the pages of Thor, while Loki possessed her body and forced her to inhabit the frame of a sick woman on the verge of death.
DeConnick told Marvel.com: "Sif hasn't gotten soft. This isn't a Rocky montage where Sif starts over in sweatpants and goes back to punching the ole' side o' beef with Mickey.
"Physically, she's recovered. It's her warrior spirit that's flagging. She's faced with an enemy here that she tries to take down with her sword, but ultimately, it's one that must be defeated with her head. If her mind's not in the right place, none of the rest matters."
The stand-alone issue will also see Sif team up with former flame Beta Ray Bill.
Sif #1, by DeConnick and artist Ryan Stegman, is out on March 24.