The Chanters of Tremaris trilogy by Kate Constable.
The Singer of All Songs (2004) The Waterless Sea (2005) The Tenth Power (2006)
Calwyn is a young priestess who chants the ice chants of Antaris. She lives inside Antaris, a community located among mountains, which is enclosed by an ice wall. The priestesses must maintain the wall with their chantments; that is, by singing certain songs, the knowledge of which is passed down to them through the temple. Nine powers can be achieved by such songs, though never by the same chanter. Legend has it that a Singer of All Songs will someday be born, who will know and use the songs of all the effects.
Calwyn is captured by Samis, who desires to heal Tremaris so that it will not be destroyed before he can conquer it. He keeps her a prisoner in the long-abandoned city-spacecraft called Spareth, which is the means by which the Voiced Ones (colonists from another planet, presumably Earth) arrived on Tremaris millennia before the story begins, trains her in advanced uses of chantment surpassing her previous abilities, and additionally reveals to her the Tenth Power mentioned by Marna. This is the Power of Signs, a code by which the songs of chantment may be written and learned. A minor romance occurs between the two of them during this time, culminating and terminating when Samis and Calwyn use their chantments to empower Spareth, sending it into interplanetary space. Calwyn, now revealed as the legendary Singer of All Songs, remains on Tremaris, while Samis flies inside Spareth, intent on reaching its port of origin.