The princess who flew with dragons - Stephanie Burgis

Sofia is the other princess. Not the crown princess - that's her perfect big sister, Katrin. Sofia is the princess who always says the wrong thing; who hates going to parties; who doesn't like people; who just wants to sit and read her books. So when Sofia is shipped off on a stomach-churning dragon flight to make another royal visit, she decides it's time for this princess to take a little break. In disguise, Sofia soon finds herself discovering a magical city of learning, new friends and freedom. In short, everything is going wonderfully
right up until it goes horribly wrong. And that's before the ice giants show up.

From the author of The Dragon with a Chocolate Heart comes a magical third adventure about acceptance, family and friendship, perfect for fans of Cressida Cowell and Cornelia Funke