Krystal Lee, a registered nurse in Twin Falls, Idaho, is reportedly being investigated in connection with Berreth's disappearance.
Berreth was last seen arriving at a Safeway supermarket with her 1-year-old daughter, Kaylee, about 12:30 p.m. on Thanksgiving. Though authorities strongly believe she is dead, her body has not yet been found. Berreth's fiance, Patrick Frazee, is charged in her murder.
Lee lives about 30 minutes from where the mother's cellphone last pinged, three days after she was last seen. A 32-year-old divorced mother of two, Lee's relationship to Frazee is unclear, but they reportedly became romantically involved after meeting at a rodeo. Police have not confirmed that they are investigating Lee.
Lee is currently on a leave of absence from her job at St. Luke's Medical Center as a pre-op nurse, the hospital confirmed.
Frazee is being held without bond at the Teller County Jail in Divide. He has not yet entered a plea to the charges filed against him, which include two counts of murder and three counts of solicitation to commit murder. He is expected to do so at a Jan. 29 hearing.
Berreth's parents, Cheryl and Darrell, have also filed a wrongful death lawsuit Friday, seeking unspecified damages against Frazee.