Maryse had been developing a preliminary plan ever since she heard about Yang Ling's intentions that night at Wissen Castle.
Just as her teacher had said, she needed to dispel Yang Ling's feeling of caution and misunderstanding of her identity if she wanted to complete her mission. Only by getting him to understand who she was could she show her true abilities and worth. Only then could she successfully drag him into the Association of Dark Magic; only then would she have the chance to obtain his trust, moving one step closer to destroying his psychological line of defense and charming him till he was head over heels for her.
Even though she could teach Yang Ling a harsh lesson using her powerful Dark Magic, turning him into a skeleton wouldn't be enough to dispel the desire for vengeance in her heart. Mercilessly abandoning him after charming him and seeing his look of intense pain was the only way to satisfy the hatred in her heart.