She grew up and had failed luck in marriages as mentioned "But I do know that Sammi is all about giving love. After all, she’s been married three times and engaged twelve. I think she’d do anything for her new family." ~ Emily Bergl on Sammi Gallagher.
When learning Frank was her father, she was upset that he withheld this but came around to the idea of having a father. She bonded with him, learning more of her family and she was pleased that he had other kids who she hoped to bond with. Sammi tried to fill in the role of big sister, though dismayed at turbulent beginnings things slowly worked out when she helps Frank with his liver problem, helps Debbie with her period, scams people with Carl, and covers for Fiona about Jimmy.
Sammi has warped view of love and family, as she shot Frank in the arm to get him to admit she needed him, called the military on the AWOL Ian, and acting as if nothing happen when returning.
Although she hopes to be seen as member of the family; Sammi shares many traits that show she is a Gallagher. This is best seen in her knowledge of scamming people, her promiscuous nature, and violent tendencies.
She was born to Frank Gallagher and Queenie Slott, her father was never in her life because he initially wanted her aborted and thought himself unfit. Samantha often wondered about her father and sought to build a relationship with him.
She lives in a trailer in a rundown neighborhood with just her young son, Chuckie. It is not revealed who fathered Sammi's son, Chuckie.
After Fiona refused to be a donor for his liver, Frank reveals the existence of his oldest child in My Oldest Daughter. The news of another sibling, greatly shocked Fiona.
In Like Father, Like Daughter, Frank with help from Carl and track her down to her trailer and she is unaware that he's her father upon meeting him, though she is sexually attracted to him and goes on dates with him.
During Strangers on a Train, Frank accidentally reveals the truth of their relationship when she informs him that she cannot give him her liver, as she is not a match. Although intensely enraged at her unintentional supposed moral crime, she tracks him down and quickly accepts him back, reconciling and bonding.
As of There's the Rub, Sammi continues to bond with Frank and goes to the Gallagher Household where she hoped to meet her new siblings but none were present. Later on, she helps him with trying to get a check for his liver surgery. Very soon, she meets one of his other children Carl and she is excited at meeting part of her extended family and introduces her son to him while he is less than pleased to have another older sister.
In Iron City, they connect more as she takes Frank to hospices but he refuses to stay and she takes him home. She becomes his caretaker and Frank explains that his estrangement from her stems from his youthful immaturity when he became a father, his initial desire to abort her, and his uncertainty about how he impregnated her mother. While she is hurt at first, she lets it go after he calls her a miracle for how she turned and has him look into hospices. Much later, she is found tending to Frank by Carl and informs of the events of their father nearly dying in the lodge, causing him to later burn it down. Sammi later meets her father's other kids (except Fiona and Ian) at the hospital to reclaim Liam, Sammi excitedly hugs Debbie when she arrives. Sammi is excited to have siblings while they are surprised their father had another daughter.
As of A Jailbird, Invalid, Martyr, Cutter, Retard, And Parasitic Twin, Sammi has taken to living with the other Gallaghers at their home where she is initially not accepted, since her siblings see her as a stranger but let her stay to tend to Frank and give her a chance though warn her of Frank's real personality. It is here where she meets Fiona, who is shocked to see her. While tending to Frank, she continues to learn about her family, finding out about her father's upbringing with his siblings and his abusive parents. Sammi later gives him drugs but he was found unconscious. When Lip finds out about her breaking this rule, he kicks her out along with Frank and Chuckie. They move into the house of Sheila, since she left for a while.
In Hope Springs Paternal, Sammi goes to get supplies for her father and meets her siblings again. She calls them out on their lack of concern to their father, even with their experience with him. Later on, the younger Gallagher children visit them and Sammi is happy when they give her a chance. She bonds with Debbie, finding it nice to give sisterly advice about her period and sex. With Debbie starting to accept her as family since Fiona had problems. Sammi thanks Debbie for letting her fulfill a role of a sister and helps Carl with a scam for money. Sammi also takes her father to Carl's teacher conference and watches him justify Carl's attack, since the bullies were insulting Liam. She states she is proud of him, as she escorts him out.
During The Legend of Bonnie & Carl, Sammi invites a paramedic to help Frank in exchange for sexual favors. After he supplies what little help he could provide, he has Sammi act on her payment and she gives him a blowjob while crying. Later, Sheila returns home and is has a request of Frank but he is not present and Sammi sees him outside trying to get to the Alibi but she stops him. When Frank states he shouldn't have looked for her, she is upset but gets him back in the house while telling him that she has something for him. Sammi brings Frank downstairs, where he finds she has invited Kermit, Tommy, and Kev to the Jackson House to help make Frank's last days great. She enjoys the sight of Frank smiling at the bar being brought to him and gives Sammi a smile as thanks.
In Liver, I Hardly Know Her, Sammi and Sheila save up money to get Frank a new liver but it turns out to be a scam and Frank's kidney is stolen As a result, Frank goes to the hospital and Sammi is present when Frank is getting married to Sheila but she is shocked to see the doctors rush him out and tell her that he will get a new liver.
In Emily, Sammi watches Carl wake Frank up and she is pleased by his recovery but confused by his delirium.
As of Lazarus, she visits her father and is happy when he wakes up. Sammi is pleased that Frank's delirium has worn off after he recognizes her and she updates him on his marriage to Sheila and new kids. Sammi later starts fighting with Sheila over who should visit Frank, before security comes and Carl sneaks in the hospital room. Afterward, Sammi and Sheila enter to find Frank is gone. Unbeknownst to them, while they are distracted by security, Carl left the hospital with Frank. At the end, Sammi moves her trailer to the Jackson House before Sheila makes amends with her by telling her that she cooked for them and Sammi accepts the gesture.
She occasionally gets into conflict with Sheila over the care of her father.
In "Rite of Passage", Sammi has taken to living with her siblings at Gallagher Household, after her trailer is destroyed. Sammi tries to help out in anyway to be accepted but is seen as a pest by them though they start to open up. Samantha tries to move her trailer but is prevented by zoning rules. Sammi gains hope when Frank promises to give her a new trailer and she is excited. She goes to The Alibi Room, where she tries to flirt with Mikhailo "Mickey" Aleksandr Milkovich but he reveals he is gay. Later on, Sammi learns from Debbie that Frank lied and sarcastically welcomes her to being a Gallagher for their father's lies.
In "Crazy Love", she takes over as the big sister and helps Fiona in caring for their siblings. She treats her father with disdain, after her eyes have been opened by the other kids. Sammi takes to bonding with the family like congratulating Debbie on entering High School and Fiona's marriage. Along with her family, she spies on Fiona and Jimmy Lishman who was surprised to learn of her. After her siblings leave when seeing Fiona and Jimmy kiss, Sammi stays to watch them. The next day, she covers for her sister when her husband shows up after Fiona had an affair with Jimmy.
Later on in Tell Me You F**king Need Me, she continues her role as caretaker for the house. She soon shoots Frank in the arm to see if he really cares about her, after he states he does she breaks down in joy while her siblings are in shock. Sammi then takes her father to get tended to at the hospital.
At the end of South Side Rules, Sammi calls the military police and tells them where Ian is. He then gets arrested and the entire Gallagher family turns on Sammi for the remainder of her time until she is incarcerated after trying to shoot Mickey.
While in prison, she is called by her son who tells her of being out of a home. Sammi tells Chuckie that someone will claim him and she is revealed to have contacted her mother Queenie Slott to retrieve him.
- Frank kept tabs on her while she was growing up.
- She is one of the few Gallagher children to call Frank "Dad".
- Although she is said to be Frank's oldest daughter, it is hinted Frank may have even more children that maybe older than her.
- Unlike her half-siblings, she has never met her paternal grandmother Peggy Gallagher who died seasons before she was introduced.
- She learned about her grandmother from her father as well as her uncles.
- She never met her step-mother Monica.
- She never met her niece Frances Harriet Gallagher and nephews Freddie Gallagher, Unnamed Nephews.
- She has had many surgeries done onto her body.
- She possesses many similarities to her siblings and father, which makes it clear she is a Gallagher.
- She is violent like them.
- She has attacked her father.
- Drinks like them.
- Will do anything for her family as seen with her father and son.
- Is promiscuous like them.
- She has been to prison like Fiona and Ian.