Sierra was a senior at Port Charles High School in season 1 before she left town after the shooting. Sierra was queen bee and enemies with Leah Corinthos and Emma Drake. Sierra was popular and was friends with Bree Brennan when she was in Port Charles and took freshman Meghan Spencer under her wing. after Leah's death, Sierra left town with her dads because they didn't believe it was safe and she hasn't been seen since. when in town, Sierra was pretty much the meanest girl in school and ran for student body president against Leah and lost to her when Leah stated that she isn't popular, she isn't doing this for popularity, she wants to be a part of the school and help make it a better place while Sierra just promised to make things amazing and glamorous.
In love with her sister Gigi's boyfriend Rex Balsom, Stacy blackmails Gigi into breaking up with him. Rex and Gigi are eventually reunited, but in the meantime Stacy and Rex have slept together, and Stacy soon discovers that she is pregnant. She miscarries after an argument with Gigi, but keeps the truth from Rex knowing that it is her only hold over him. Stacy plots to get pregnant again by someone else in order to pass the baby off as Rex's. She drugs ex-boyfriend Schuyler Joplin and attempts to sleep with him, but he refuses her. She only becomes pregnant again after seducing a drunken Oliver Fish, but tells Schuyler that the baby is his. Schuyler agrees to keep the truth from Rex so that he can have Gigi for himself. Rex's crazed biological father Mitch Laurence kidnaps Stacy in February, intending to raise her baby as his heir; when she reveals that the baby is not Rex's, Mitch abandons Stacy in a blizzard. Gigi finds her, takes her to a cabin, and on February 11, helps Stacy deliver a baby girl she names Sierra Rose after Stacy and Gigi's childhood dolls. Gigi rushes off to the hospital with a newborn Sierra; Stacy tries to follow, but falls through the ice of a frozen lake. Despite Rex and Oliver's attempts to save her, she disappears beneath the ice and is presumed dead. Sierra is soon diagnosed with a congenital heart defect requiring immediate surgery; now aware that he is not the baby's biological father, Rex defers to Schuyler to approve the surgery. On April 2, it is revealed to Gigi, Schuyler, and Rex that the baby's real father is Oliver. He is soon awarded legal custody.
In The Series
Sierra is seen first in 1.01 Pilot, she walks up to Leah Corinthos and Emma Drake and tells them to not bother running because she will win and be the ultimate queen bee of PC High. Later Sierra is seen handing out candy that says "Vote For Sierra" on it. during the debate, Sierra later gives her speech saying all the great things she can do for the school like make dances fun and stuff like that while Leah talks about the real problems, When it comes time for voting, Sierra votes for herself and loses the election to Leah.
1.06 The Party Scene, Sierra goes around school promoting the party she is having while her dads are out of town. She also says that Leah Corinthos and Emma Drake are not invited. At the party she is seen drinking and hanging out with Bree and when Leah comes to get Briana, Sierra is mad she came and tells her to get out.
1.14 Falling Inside The Black, Sierra is seen at the dance with Bree saying that The Pretty Reckless sucks
1.17 Nothing Left To Lose, Sierra skips school