Felicia Day returns to Supernatural in the January 23 episode which is titled "LARP And The Real Girl."
Here's how The CW describes it:
FELICIA DAY RETURNS! --- Sam (Jared Padalecki) and Dean (Jensen Ackles) investigate the mysterious deaths of two LARPers (Live Action Role Playing) who were playing a game entitled Moondoor. The guys are thrilled to discover the Queen of Moondoor is none other than Charlie (guest star Felicia Day). The three learn that a fairy (guest star Tiffany Dupont) has been commandeered to harm people and the only way to stop her is to find her master. Jeannot Szwarc directed the episode written by Robbie Thompson (#811).
The network has now released some promo shots, which you can enjoy below: