Wren to the Rescue

Wren to the Rescue is a novel by Sherwood Smith, which she first wrote in high school in the mid-1960s under the name Tess's Mess. Described are the adventures of the title character, Wren, a female human orphan whose best friend Tess is revealed to be the princess of a neighbouring country. When Tess is kidnapped, Wren races to her rescue, making friends with students from a Magic School and learning about her own talents along the way. As part of her adventure, Wren is transformed bodily into a dog, and must decide whether to abandon her quest or try to turn her new shape to the advantage, at great risk of losing her human identity in the process.