Avalon: Web of Magic Book 12, Full Circle by Rachel Roberts

Avalon Needs a Hero! It started with a quest to find the home of all magic: Avalon.

It may end in darkness.

Three girls, Emily, Adriane, and Kara, their fates set long ago, were to become mages. They were to discover the secrets of Avalon and save their animal friends.

They failed.

Now, the Gates of Avalon are locked, beloved friends are doomed, and the Dark Sorceress reigns supreme.

There may be one final chance to fulfill their destiny. But it will take the strength of a warrior, the fire of a blazing star, and the heart of a healer.

The mages must put everything they love on the line―and be prepared to sacrifice all―as the final battle for Avalon begins!