Kristen Johnston has been promoted to regular for the upcoming seventh season of Mom, SpoilerTV has learned. She plays Tammy, an ex-con who happens to be Bonnie's foster sister for a short time in their teens. They reconnect after Bonnie comes across Tammy while visiting a women's prison and joins Bonnie's gang of sober women after she gets out of prison.
Johnson first appeared on Mom for one episode in season 5 and had been heavily recurring in the 6th season.
Season 7 of Mom premieres September 26th on CBS.
