She was played by Venus Terzo, who also played Valeria Crossley in a fifth season episode of Psych.
Sonja was Melissa's (the episode's protagonist) hairdresser, as well as an evil and powerful White Witch. After Melissa vents about her problems with her marriage, Sonja gives Melissa a spell to ensure that her husband, Dan, remains in love with her. In actuality, the "spell" is really an ancient curse, and it is activated when Melissa kisses Dan, who passes the curse to his mistress, Staci, when they kiss. After the deaths of Staci and Dan, Sam and Dean head to the salon, where Sam encounters Sonja. Sonja stated that she originally set to punish the unfaithful husbands, but she then decided to tweak her magic to punish the women who go back to their husbands, hence why she targeted Melissa. Sonja later attempts to kill Sam, only to be confronted by a knife-wielding Melissa. She is later shot to death by Sam.