|“||Maybe it's a sign, Arthur... Try. Try to do the good thing.||„|
|—Mary-Beth comforting Arthur|
|“||A kind, good-natured young woman, which makes her the perfect criminal. By the time people realize they’ve been duped, Mary-Beth is already on her way home with the money.||„|
|—Description by Rockstar Games.|
At some point prior to 1899, Mary-Beth got into trouble when she stole watches and wallets from several men. She was found by the Van der Linde gang while being chased by her pickpocketing victims, and was presumably rescued by them before joining the gang. 
Events of Red Dead Redemption 2
Horseshoe Overlook Chapter
Mary-Beth goes to Valentine with Uncle, Arthur, Karen, and Tilly to look for possible leads. Mary-Beth soon finds a lead on a lucrative train robbery. Later, she and the other female members of the camp can talk to Arthur about his recent events.
Clemens Point Chapter
Mary-Beth can assist Arthur and Sean in robbing a stagecoach. She distracts the drivers to allow Arthur and Sean to attack it. At the end, she is captured but Arthur saves her by killing the guard who held her hostage. Afterwards, she, Arthur and Sean divide the money between themselves and return to camp.
Saint Denis Chapter
Not long after setting up camp at Shady Belle, Arthur comes across Mary-Beth reading and goes to talk with her. After talking about their pasts over a cigarette, Susan Grimshaw interrupts them about the disappearance of Tilly Jackson. Not long afterwards, Mary-Beth screams upon witnessing the mutilated corpse of Kieran Duffy enter camp on horseback as the O'Driscolls attack the gang. She later expresses her grief over his death.
Beaver Hollow Chapter
Arthur can tell Mary-Beth that he is terminally ill, diagnosed with Tuberculosis. Mary-Beth gives him her sincere condolences, but tries to cheer Arthur up by encouraging to make his last moments count.
As the gang begins to fall apart due to Dutch's increasingly erratic behavior and decisions, Mary-Beth eventually leaves alongside Simon Pearson and Uncle. A furious Dutch informs Arthur of the trio's departure.
Mary-Beth's encouraging words to Arthur can be one of the lines he reflects upon during his last ride.
By 1907, she has become a romance novelist under the pen name of Leslie Dupont, and is seen writing a book in the credits. John Marston can encounter her at the train station in Valentine, where the two talk about their new lives, while also reminiscing about their old lives and Arthur. When a train approaches, Mary-Beth gives John a copy of one of her books, "The Lady of the Manor", and the two bid farewell as she boards the train. A letter from Tilly reveals that she and Mary-Beth are in close contact and still see each other often.
Mary-Beth presents herself as a kind and good-natured woman, though this is but a smokescreen to fool and manipulate her targets. Behind her lady-like persona, Gaskill is considered the perfect criminal (paraphrased from Rockstar Bio). Towards the gang, however, she is truly loving and considers them her family. Mary-Beth is a devout bookworm, almost always seen reading a romance novel at camp, and even becomes a writer herself in the epilogue, albeit a very self-deprecating one. She's insecure about her passion and always gets shy and bashful whenever someone asks about it, calling her own books "silly".
Despite her criminal ways and tendency to commit crimes, Mary-Beth is considered the kindest and most gentle member of the Van der Linde gang, seen during many moments throughout the story, as Mary-Beth would often offer to speak with Arthur about recent events and offer him comfort on his inevitable death by his illness. Her kindness also extends towards strangers and possibly threatning figures, as seen during random events in the camp, Mary-Beth gives Kieran a cup of water while the latter remains tied up in a post after witnessing Karen taunting and mocking him.
Mary-Beth is a young, freckled woman, with brown hair in two pigtails, and blue eyes. Mary-Beth usually wears a purple (or green) blouse, a golden necklace, a brown belt with a golden buckle, a dark green shawl, a maroon skirt with two white stripes at the end, and a black boots.
By 1907, her appearance has changed very little.
- Red Dead Redemption 2
- "Outlaws from the West"
- "Enter, Pursued by a Memory"
- "Eastward Bound"
- "Polite Society, Valentine Style"
- "Blessed are the Peacemakers"
- "The Battle of Shady Belle"
- "Angelo Bronte, A Man of Honor"
- "No, No and Thrice, No"
- "Horsemen, Apocalypses"
- "That's Murfree Country"
- "Visiting Hours"
- "A Rage Unleashed"
- "Red Dead Redemption" (voice only)
- "American Venom" (credits)
- If the player boards the train that Mary-Beth leaves on, she is nowhere to be found.
- It appears that Dutch has a crush on her; he can be seen flirting with her and asking her about her books on multiple occasions, much to Molly's dismay.
- She is the kindest member of the Van der Linde gang to Kieran when he is captured, giving him water without any cruelty. She also engages in two additional conversations with him after "Paying a Social Call", and is later seen mourning his death, showing the possible romantic interest between them both.