From Our Catalog:
The wind singer: an adventure by William Nicholson, 2000
Book description: After Kestrel Hath rebels against the stifling rules of Aramanth society and is forced to flee, she, along with her twin brother and a tagalong classmate, follow an ancient map in quest of the legendary silver voice of the wind singer, in an attempt to heal Aramanth and its people.
This is the first book of the Wind on fire trilogy. The other titles are Slaves of the Mastery: an adventure and Firesong: an adventure.