Warning: The following contains SPOILERS for Yellowjackets.
While Yellowjackets is bound to have many more deaths as the series continues, this particular one affected Shauna enough to completely change her character. Teenage Shauna (Sophie Nélisse) definitely made some questionable choices throughout the first season. Between getting pregnant by Jackie's (Ella Purnell) boyfriend and her taking Lottie's side during the Doomcoming it's no secret that she hasn't been a beacon of example. Her choices don't seem to improve in her adult life, as she has a secret affair with Adam and isn't the kindest to her teenage daughter. With all of that being said, her poor decisions in her adult life are actually informed by a specific character's death.
Despite her bad teenage judgment, the younger Shauna has plenty of potential and prospects. She's smart, fiercely independent, and tries to remain loyal to what she feels is right. That being said, the Yellowjackets season 1 ending brought a deep tragedy to her life that sheds more light on her adult character. When comparing the teen Shauna and the adult version it's clear that she's settled into a life that doesn't fit her previous prospects. As well, the adult Shauna appears to be much colder and more calculated than her younger self. While some of this can be attributed to her traumatic time in the woods, it's also due to the circumstances of a particular character's death.
The adult Shauna is plagued by crushing guilt over her best friend Jackie's death, so much so that it changed her entire character and consistently informs her decision-making. In the Yellowjackets season 1 finale, Jackie is left to die out in the cold, and Shauna is given the option to let her back inside but chooses not to. Based on Shauna's heartbreaking reaction she feels responsible for her best friends' death. Her seemingly cryptic behavior as an adult is explained by Jackie's passing. This shame plays a major role in her relationships in particular. Shauna's coldness towards her husband Jeff (Warren Kole) is because of the guilt she feels over "stealing" him from Jackie and then throwing it back in her face during "Sic Transit Gloria Mundi". Her relationship with her daughter also follows this pattern. Shauna claims she "doesn't like" her daughter, and it's because Callie (Sarah Desjardins) is a tangible reminder of what she did to her best friend.
While other Yellowjackets survivors see things like Taissa's "Man with No Eyes", Shauna only sees Jackie's ghost. This shows just how much her friends' death affected her, as it's one of the few visions she carries back with her from the woods. Just like how Shauna's relationship with Jeff and Callie is affected by Jackie's passing, so is her relationship with Jackie's parents. For her friends' parents to be welcoming enough to allow Shauna into their home after what she did is more than kind. Shauna repays them with coldness, a survivalist exterior developed by the tragedy of Jackie's passing.
While SHOWTIME's Yellowjackets is primarily a Lord of the Flies adaptation centered around a girls' soccer team's survival, it's also heavily focused on relationships. Other relationships that are explored include that of Natalie and Travis, as well as Taissa and Van. The unique horror/drama series left bombshell after bombshell in the wake of the season finale. Yellowjackets' cast of characters will hopefully return for season 2, along with a new villain in the form of the adult Lottie Matthews.