Tammy Diffendorf
Tammy Diffendorf.jpg
Gender Female
Nationality American
Played by Kristen Johnston
Job Co-Owner of PlunkenDorf Construction
Waitress at AJ Barrelworks
Prisoner (formerly)
Family Claire Dickinson (Ex-Foster Mother)
Frank Dickinson (Ex-Foster Father) (Deceased)
Bonnie Plunkett (Ex-Foster Sister)
unnamed (mother) (Deceased)
unnamed (father) (incarcerated)
Cookie (aunt) (estranged)
Episodes 57
First Seen "Crazy Snakes and a Clog to the Head"
Last Seen "My Kinda People and the Big To-Do"
Seasons Season 5Season 6Season 7Season 8

Tammy Diffendorf is Bonnie's ex-foster sister and a main character on Mom. She is portrayed by Kristen Johnston.


Tammy first appeared in Season 5's "Crazy Snakes and a Clog to the Head". In "Triple Dip and an Overhand Grip", the foster mother mentioned that Tammy's father killed her mother before she ended up in foster care. She was in a foster house with Bonnie until Bonnie got her kicked out and she spiraled down an illegal path and eventually landed in prison. After Bonnie stole their foster father's wallet and planted it in Tammy's bag, their foster father kicked Tammy out. She landed in prison because she robbed an Outback Steakhouse (she was trying to steal steaks on a "Cops Eat Free" night, and was arrested by 32 people). She and Bonnie reconnect after she gets out of prison in "Big Sauce and Coconut Water", and she temporarily stays with Bonnie and Christy before moving in with Marjorie.


Season 5

In "Crazy Snakes and a Clog to the Head", the girls go to a prison and give speeches about why they are in A.A. Meetings and how they recovered. Bonnie stands up to tell her story, she mentions her name and that she is an alcoholic. Tammy stands up immediately and shouts "Bonnie Plunkett?!", then charges at her as she says "you ruined my life!". Having no idea who this person is, Bonnie is obviously shocked and confused. Everyone panics and the guards call for backup. Jill stands on a chair and states that she is about to die in a women's prison.


After the commotion, the girls go home, on the car ride Bonnie tries to remember who Tammy is stating "Tammy? Tammy. Who the hell is Tammy?", we see her in different situations, still trying to remember who Tammy is by repeating the name over and over. The girls are at The Bistro, in their booth, and when Wendy is about to tell her story, Bonnie exclaims "Oh, my God! Tammy!", meaning she has figured out who Tammy is. Marjorie tells everyone that Wendy should finish her story, however Jill interjects with "Oh come on, Marjorie, a gigantic woman tackled Bonnie, tell me you don't want to hear the 'Who? What, Why?'". Bonnie tells the story of how she ruined Tammy's life, taking Tammy from good girl, to bad girl in prison.


Bonnie heads back to the prison and reads a written apology to her, but to Tammy, she is only apologizing for the minor things. Tammy says "Let me get this straight, you drove all the way out here to apologize to me for handing me a joint and messing around with my boyfriend?...When are you gonna apologize for what you really did to me?" Tammy sees that Bonnie doesn't know what she actually did and tells her that she set her up. Tammy states "You got me kicked out of that house!", Bonnie fires back "No, no, you got yourself kicked out, cause you stole our foster father's wallet!", Tammy says that Bonnie "stole his wallet and planted it in my book bag", and Bonnie realizes slowly that she was the one who did it.


Tammy states that she spent the last 40 years wishing she had never met her. Tammy walks up and leaves, Bonnie contemplates how much she damaged her and ruined her life. She feels genuinely guilty and brings her daughter in as a lawyer (studying to be a lawyer) to see, legally, what she could do about the situation. It isn't solved in the episode, however it is implied that Tammy forgives her and they talk it out while reminiscing.


After she gets out of prison in "Big Sauce and Coconut Water", Bonnie convinces her to stay with her instead of going to halfway house. She remains there shortly before moving in with Marjorie.

In "Triple Dip and an Overhand Grip", Bonnie and Tammy take a trip to their old foster home to make amends to their former caretaker, Claire. It was revealed that Tammy's father killed her mother before she ended up in foster care.

In season 7, she is promoted to a main cast member.

Appearances (Table)


 1   2   3   4   5   6   7   8   9  10 11 12 13 14 15 16 17 18 19 20 21 22 Total
Season 1 0
Season 2 0
Season 3 0
Season 4 0
Season 5 1
Season 6 18
Season 7 N/A 20
Season 8 N/A N/A N/A N/A 18
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