The Silver Dolphin Mermaid Curse Series, Book 1.

Lizzy Baxter is thrilled when her family moves to Cornwall-she's always loved the beach. Lizzy doesn't realise, but she has a special connection with the sea-and the mystical mermaids and silver dolphins who swim there. But there's much more to the beautiful blue-green world than magic. The veil sea queen is plotting to steal something precious-something that belongs to Lizzy. The Mermaid Curse is a perfect blend of fantasy and reality