When Anna and Stacey were young, they were best friends and did everything together. However, by the time they reached high school, Stacey becomes a cruel bully and went from being Anna's friend to tormenting her for fun and popularity status. However, she still managed to convince Tess that she and Anna were still friends and their fights were just friendly feuds.
Role in the film
Stacey is Anna's archival and former best friend. She always likes to torture her and tries to get her into trouble. One day in P.E., she hits her on the head with a volleyball, Anna throws it back at her, and ends up in detention for doing so. The next morning, when Anna tries to say hi to Stacey, she and the girls pretend to hug Anna but fold up her shirt causing her to fall backwards over a bike rack and Stacey tells the girls to run away. She also pretends to make up with Anna and asks her to sit with her during a test.
When Anna (with Tess in her body) is taking the test and Stacey writes a note to Tess that she's glad to be friends again, it turns out that it was a trick since the note was on Stacey's test and she tells the teacher that Anna's copying her test so it would look like Tess is cheating, gets her into detention, and then she sees the kind of person that Stacey has become.
Later, Tess gets revenge on her by gaining access to the staff lounge by Jake, a young staff member who Anna has a crush on, to finish her test. Then Tess erases all of Stacey's answers and writes "I'm stupid" in their places. It's unknown what actually happens with Stacey later on. However, in a deleted scene, she confronts Tess (while still in Anna's body) and Tess punches her in the nose for payback and she reacts to her nose getting messed up. She is not seen again afterward, so it is unknown if she reformed or not.