[Harry Potter] Help, I'm a Slytherin NPC

(I'll write when I have time. Feel free to unfollow. Thanks for understanding.) She discovers that she is a Slytherin NPC in the Harry Potter series: a character with no thoughts, no backstory, and no role in the plot, just another face in the background at Hogwarts every day. Whether she's pulling old Dumbledore's beard, causing trouble in Snape's class, or failing to hand in Professor McGonagall's assignments, no one gives her a hard time! They won't even remember her, and everything will reset to follow the plot. She does whatever she wants, even selling snacks whenever the protagonist with the lightning scar gets into an argument with Slytherin! Then she gets caught. The person who catches her has messy black hair, and anger flashes in his emerald eyes behind his glasses. He grabs her arm, panting. "What's your name? Why are you doing this?" She thinks for a moment, puts on a stereotypically sneering expression, and delivers the standard reply with perfect diction: "Well, if it isn't the famous Chosen One! What, isn't the House Cup enough for you?" # Harry finds it strange. At some point, he starts seeing a Slytherin student who... doesn't act like anyone else? He asks Hermione, but she says she's never seen this person. So the girl who dumped a failed potion on Snape in class doesn't exist? Could he be imagining her because he hates Snape so much? He has to find the truth and prove he's not crazy. At last, he gets a chance to corner her and ask. But then she acts just like any other Slytherin. He can't accept it, so he goes after her again. She: "Well, if it isn't the famous..." He cuts her off, knowing exactly what she'll say. "Stop pretending. You say the same thing every time!" Reader's note: Some inspiration came from Extraordinary You. Theme: Everyone is the protagonist of their own life.