"Because I'm a childish princess that has been coddled and had everything I wanted handed to me my entire life, so I deserve the powers SHE has! SHE deserves to die for having special powers that should have been MINE!"
- Spoiled brainless brat.
Jealousy is a powerful motivator. And to be fair there are plenty of people who are self destructive knowing how damaging their actions are.
She probably thinks they can just find someone else to replace the MC
And that replacement will still have more power than her and the jealous will just restart
"I'm gonna kill the one person keeping the entire ruse intact and stopping people from realizing that i am a scam"