[Miranda_]

No, no and no again. I'm sorry, but your character is not only a Mary Sue, but also what is known in the Harry Potter fandom as a "B*tchiwitch". In other words, cruel, evil, misunderstood... far too cliched. Even the Slytherins have good points; no-one in the Harry Potter universe cept for Voldemort is completely bad. So your character is unrealistic. Also, Slytherins are not chosen cuz they're "spiteful, cruel and stubborn"; they're picked for being ambitious. There are nasty people in all the houses; for example, James Potter and Sirius Black were nasty bullies, and Cho's friend was a tell tale. Please redo your character, not only to be more realistic, but to not be a total cliche stereotype.