Mariana is Jesus's 15 year old twin sister and was taken in along with him by Lena and Stef, and later formally adopted by them. She is very smart and girly, and cares about her appearence very much. She's popular and social, but also very naive when it comes to certain topics. Such as, reconnecting with the mother who abandoned her and Jesus at a very young age, and stealing Jesus's pills and selling them to earn money that Mariana can give to her mother. After Mariana's drug trafficking begins to unravel, one of her friends is caught sniffing up the sold drugs and, to defend Mariana, blames the trafficking business on Callie. Mariana let's Callie take the blame but soon her guilt builds up and she decides to tell her mothers. Before she can, though, Jesus takes full blame and responsibility for all the actions with his pills, clearing both Mariana's and Callie's names. She speaks spanish fluently and likes to gossip, especially about Callie.
Jesus and Mariana are very close, but she kept some secrets from him which he is soon found out. It is revealed that she has taken his pills in order to get money to visit their birth mom, who he doesnt want to see again. They eventually come together when they need each other most.