Tiara Friends: the Secret of the Silk Dress (Tiara Friends) -- Paperback / softback

Best friends Millie and Jess look just like twins! Millie is a princess and Jess is a maid so they have lots of fun swapping dresses and going on adventures around Peveril Palace. When Millie's snooty cousins come to stay, a silk dress goes missing. Can Millie and Jess work out who took it, before the wrong person gets the blame?