Sierra's Friend

Sierra's friend is a teenage girl who attends the same school in Jasper, Nevada, as Sierra and Jack. She's presumably a troublemaker, and she hangs out with Sierra a lot.

Darkness Rising, Part 1
Sierra and her friend encountered Jack outside KO Burger, apparently talking to his motorcycle. Amused, Sierra's friend watched a flustered Jack attempt to flirt with Sierra, until two purple cars appeared and tried to run them down. Sierra and her friend screamed and jumped out of the way.

Deus Ex Machina
Sierra's friend ended up in detention with Miko one time.

Speed Metal
She was again hanging out with Sierra again after school when they spotted Jack on his motorcycle. Sierra tried to ask for a ride, but after Vince interrupted them, her friend whispered something to her that they both found amusing. Vince challenged Jack to a street race, and both Sierra and her friend went with them to be spectators. Following Jack's win, they spread the news of his victory around the entire school.

Out of His Head
Sierra's friend sat in the desk in front of Jack during one of their classes.

Operation: Bumblebee, Part 1
She was talking with Sierra outside the school when Raf Esquivel was picked up by an ambulance belonging to a friend of Jack's mom.