It's time, Cassandra Klein

Fantasy novel for older children in the Takeaways series. When Cassandra receives an ugly necklace for her birthday from her long-lost mother, she is reluctant to try it on, but when she does she finds herself in a startling new world. She is transported to Morphea, a place where the myths and legends of our world are true, and she must decide between the mysterious pull of her mother, and rescuing her father