One of the seven deadly sins- Envy is a feeling of grudging admiration for another's talent, integrity, personality, looks, money or happiness.
Envy oftens serves as the motivation for different acts.
Envy may lead one to avoid, to dislike or to insinuate the so called superior person is bad to make others think badly of them. They wish for the other person to not have whatever they are envious and go to extreme measures to prevent them from having it. If they can't get it they are satisfied with trying to destroy thier happiness through under-handed means.
He didn't want to see her happy so he set up a plan to attempt to bring her unhappiness.
She had envy in her heart of the girl who always beat her talent-wise so she set out to make everyone hate her through lies, manipulate measures and deception.