If the Magic Fits by Susan Maupin Schmid

When 11 year old Darling Dimple is promoted from working in the kitchen to ironing for the princess, she learns that closet number seven holds 100 old dresses, which she later learns are magical.  Each dress transforms her so that she looks like someone else, which she needs to do in order to save the princess from marrying an evil prince.  The book is a fun read and I think that upper elementary and middle school age children will enjoy it.