I meant this trinket -
From an old druid crone who was part of Aridha's ceremony she receives a thin silver chain with an odd medallion. There is an amethyst at the top where the chain feeds through and a silver crescent moon pendant, grooved down its inner side to hold a small round very clear mirror. The whole piece looks like a full moon on a chain. "When you look into it young one," the elder druid says raising her hood. "You will always see yourself for who you truly are." She then walks away.
The mirror only shows Aridha's reflection when she looks into it and reflects nothing else, looking like a piece of white metal to anyone else. When she wildshapes the medallion can neither fall off or merge with her form.