My trump card
Selvih didn't understand why her heart hurt so much it felt like it was about to explode. She immediately realized that someone was using magic to curse her.
Although Selvih didn't know who was using the curse magic, she guessed that it was definitely Bryen.
Although Bryen was from the Ancient Kingdom, her magic ability was not as high as Selvih's, but Bryen had another kind of ability which was curse magic.
Yes, Bryen was very good at curse magic, as long as she had someone's hair or some other belonging of the person that could be cursed, Bryen could use high level curse magic to curse that person.
In this case, Bryen only needed a few strands of Selvih's hair to use her curse magic, Bryen's spell caused Selvih so much pain that She was unable to use magic.