The Naming by Alison Croggon

Maerad, a slave in Gilman's Cot is found by Cadvan, a Bard and rescued. They escape and Cadvan discovers that Maerad is the daughter of Pellinor, a school of Bardom that was ransacked and burned. Cadvan believes that Maerad is the Foretold who is come to save the kingdoms. He must take her to Norloch to be trained in her magical powers. On their travels they meet terrible monsters from the Dark and are almost killed. Along the way, they find Hem, who turns out to be Maerad's brother. Although the First Circle of Bards won't accept her, Norloch makes her a Bard and Cadvan and Maerad escape just in time before the city is burned.
This is the first book in the series of The Books of Pellinor. Although it is long, it is a good story. Sometimes too much description, but it leaves you wanting to read the next book.
The books in the series are: The Naming, The Riddle, The Crow, The Singing.