The Tiara is an accessory item in Nintendogs and its 3DS successor. It is a silver tiara with shiny pink jewels. It can be found during walks in Nintendogs: Dachshund and Friends and sells for $30 in the Secondhand Shop.
DS: "Who doesn't love princesses? With this bejeweled tiara, your pup can feel like one!"
3DS: "With this bejeweled tiara, your pet can feel like a princess!"