In Faery Rings, the Truth of Things — Dayle A. Dermatis

Teenager Anwyn Glas goes by Annie to avoid being teased by her peers in Tuscon, AZ. But when her mother drives across the Severn Bridge into Wales with Anwyn and her brother, Ewan, Anwyn decides maybe her name fits her. When they reach the old family cottage and walk through the woods to a mysterious circle in a meadow, Anwyn discovers just how much she had to learn about her magical Welsh heritage.