
Girl can just use her powers so subdue him lmaooo if she's worried that he'll spread it then best she can do is damage his throat so he'll never be able to talk or threaten him. What's the use of your powers girl

Well for one thing she didn't know if he was the only person sent. After all it is her stepsister.. or even her stepmother behind it.
To her If she knew it was only her stepsisters work, she might have used her power. But she cant be 100% sure her stepmother didnt have a hand in it, as her stepmother hates her guts and would send assassins.
After all she can be 100% sure her "sister" ran crying to her "mother" after she slaped her.

She was given her power because she was pure, kind, caring and inocent, she had to promise to not use it out of spite or to hurt others.
But at the same time its a god like power, and if it comes out that she has said power, she becomes a walking target for all nobels, kingdomes and bad guys.
+ We are informed she was given the power without the "fairy queens permision, she has only been alowed to keep it because she hasnt abused it.
The second she uses it for hurting someone = fairy queen taking it back as it is a power they protect for the god.
Noooo I can't wait for another 10 days to see the duke's reaction!