Odd Girl Out

Vanessa Snyder (Alexa Vega) is a well-respected eighth grader in her school. She has a loving single, divorced mother, Barbara (Lisa Vidal), who is proud of her academically and socially successful daughter. Vanessa is also "in" with the popular clique, which consists of her best friend Stacy Larson (Leah Pipes), the queen bee, and Nikki Rodriguez (Elizabeth Rice), who is secretly jealous of the bond between her two friends. On the exterior of the circle is the outsider, Emily (Shari Dyon Perry), and the "wannabe," Tiffany Thompson (Alicia Morton), who is dying to make it into the group.
One day, Nikki tricks Vanessa into getting close to Tony (Chad Biagini), a boy whom Stacy (and somewhat Vanessa) has a crush on. A web of lies, nasty rumors, and manipulation ensues, and Vanessa is ostracized by the clique for "backstabbing" Stacy. Nikki gets Tiffany accepted into the clique, and Tiffany becomes Nikki's sidekick at bullying. Although Nikki is the main bully, Stacy plays her part by pretending she's still Vanessa's friend and not stopping the attacks. Vanessa is slowly pushed out of class activities, socially isolated and her tormentors create a website that bashes her.
Although Emily tries to convince Vanessa not to go running back to the clique, Vanessa keeps attempting to seek reconciliation with Stacy, to disastrous results. One day, Vanessa tries to sit with the girls at lunchtime, but they reject her. Vanessa runs off into the girls' bathroom, and hides inside one of the stalls. The girls follow her in and verbally assault her until she cries. That night, Vanessa walks into her bathroom in her underwear where she suffers a nervous breakdown and chops most of her hair off. Then she starts skipping school, fearing the agony in the hallways. Stacy offers a fake truce to Vanessa, making it look like Vanessa copied one of Stacy's assignments when it was in fact vice versa.
Once Barbara sees printed-out disdainful comments about Vanessa's hair, she tries to help by informing the school about the bullying. Principal Jessup states that she is unable to take disciplinary action against verbal abuse. Barbara even tries to reason with Stacy's mother, Denise (Rhoda Griffis), but only ends up straining their friendship.
Vanessa's spirits are suddenly lifted when she is invited to Stacy's birthday party. After getting all dressed up, she and Barbara arrive at a nightclub that Stacy had claimed to be the location of the party, but it turns out that there was no party at all. After returning home, Vanessa goes ballistic and later attempts suicide by taking an overdose of Barbara's sleeping pills, causing her to pass out on the bathroom floor. Barbara soon discovers this and immediately calls an ambulance. As Vanessa is being put into the ambulance, a boy from her school records the incident. Vanessa is taken to the hospital and treated.
In the hospital, Barbara reveals to Vanessa that she was also bullied when she was a teenager, which causes her to encourage Vanessa to stay friends with Stacy. She says that she never personally dealt with it and wishes that Vanessa would stand up for herself. Nikki and Tiffany insult Vanessa even after she attempts suicide; they watch a video of her being taken to the hospital and call her a "druggie" and a "pathetic loser." During a class session, Emily accuses Stacy of nearly killing Vanessa by her actions. She is also the only one of Vanessa's classmates to visit her in the hospital and befriend her. Back home, Barbara spots malicious instant messages popping up on Vanessa's computer and sends them to Principal Jessup. The culprits are Nikki, Tiffany, and Ezra (Joey Nappo) and are told by Principal Jessup that a new policy against cyberbullying student harassment is now being enforced at the school after what happened to Vanessa. She then gives them the ultimatum: If they admit that they have been cyberbullying Vanessa, they would only be suspended for a week. But if they don't confess, they would be expelled from school and will not graduate with their class.
When Vanessa returns to school, Stacy convinces her that she's sorry about the bullying, reuniting them both. They IM each other about how great it is to be best friends again. Then graduation day comes and the final dispute happens after the ceremony - Nikki and Tiffany derisively read the chat between Vanessa and Stacy, which Stacy had sent to Nikki, who printed it out, aloud in the crowded hallway. Vanessa confronts Stacy in front of the whole class, bringing everything down on her and sees right through her lies. Humiliated, Stacy flees the school in tears and her two "henchwomen," Nikki and Tiffany, are left powerless without a leader. The class applauds Vanessa as she hugs Emily, her only true friend. Barbara, who witnessed the whole exchange, watches with pride as the two friends leave for an after-party, permanently disbanding the bullying clique.

Question: What is the (assumed) reason that Vanessa left school?
Answer: Stacy was bullying her.