|“||You said he'd win the game. You're a fake psychic, fake-psychic boy!||”|
|— Sienna to Booker|
Sienna is portrayed by Jenna Davis.
Sienna is popular and influential, especially through the social media app, Peanut Face where she has a lot of followers who follow her and whatever she likes. She is sweet and loves dogs as seen in how much she cares about her dog, Mr. Manchego. Sienna is aggressive and seems to result to violence when someone messes with her as seen in the way she leads other students to attack Booker for being a fake psychic and how she aggressively demands her money back from Nia and Tess.
Sienna because Levi's pal on Peanut Face which influences a lot of her friends to follow Levi too. When Booker gets a vision of Sienna's puppy stuck in the rooftop, he takes advantage of the situation to rescue the puppy and get Sienna's follow. He asks Sienna something bad is going to happen to the dog but Sienna doesn't believe him until her mom calls in saying the dog is lost. Sienna is devastated but luckily Booker saves the day by rescuing Sienna's dog, Mr. Manchego.
Sienna starts suspecting that Booker stole the dog because first he said something bad would happen to the dog and then he rescued him. She starts calling Booker a puppy stealer, which pushes Booker to tell her that he's psychic. At first, Sienna doesn't believe him but after seeing that Mr. Manchego likes Booker, she believes him. She promises not to tell anyone. But then, she posts about it on Peanut Face, causing all the kids at school to start calling Booker psychic. Later, Sienna joins the rest of the crowd in getting fake visions from Booker. After finding out that Booker is telling them fake visions, Sienna leads the rest of the kids to run after Booker and Nia.
Sienna is fascinating by Nia's jacket and says that she would do anything to wear it. This gives Nia an idea to start renting the jacket for money. She pays to rent Nia's cape the next day before detention; but she returns it and demands her money back after noticing the new trend from Zeena. When she buys one of Nia's malfunctioning cell phone pouches, she demands a refund and even threatens to beat them up if they don't give her money back.
- As revealed in "Because", she likes avocado toast.
|“||Mr. Manchego just doesn't give kissie-wissies to just anybody.||”|
|— Sienna to Booker|