I'm trying to figure out the title and author of a young adult fantasy book I read part of a while back.
Reading level: suitable for a 12-year-old
Publication date: before 2001
Plot: The protagonist is a girl descended from some tribal folk up in the hills. The leader of the tribal folk comes to visit her town. Some sort of magic runs in his bloodlines so that the townsfolk can't sustain eye contact with him without suffering harm. The protagonist stares him down and faints as a result. When she comes to, she finds that he was surprised she was able to hold his gaze for so long and that she must be a part of his bloodline.
She journeys to the hills with him and takes part in some sort of sword tournament where the goal is to cut off your opponent's belt. She cuts off the belts one opponent after another until a final mysterious opponent (who turns out to be the tribe leader again) cuts off her belt. At first she is angry that he beat her; then she talks to another member of the clan who still wears his old belt, sewn back together, because he is proud to have been defeated by such an esteemed opponent.
[After that point, I'm fairly certain I skimmed most of the remainder of the book, so the details are blurry.] The girl learns that the power in her bloodline is used for destruction but that in ages past it was used for healing. There's some sort of battle where a lot of people are injured, and she learns to use the power to heal people again. (There may have been a feminist undertone of her being the first female to have the power in many years and thus being the first with the ability to heal rather than destroy.) I think I remember her sending out blue waves of energy, but I don't recall whether those were waves of healing or destruction.
What book is this?