Dragon slippers / Jessica Day George.

Enhanced descriptions from Syndetics:

Poor Creel. She can't believe her aunt wants to sacrifice her to the local dragon. It's a ploy to lure a heroic knight so that he will fight the dragon, marry Creel out of chivalrous obligation, and lift the entire family out of poverty. Creel isn't worried. After all, nobody has seen a dragon in centuries.

But when the beast actually appears, Creel not only bargains with him for her life, she also ends up with a rare bit of treasure from his hoard, not gold or jewels, but a pair of simple blue slippers-or so she thinks. It's not until later that Creel learns a shocking truth: She possesses not just any pair of shoes, but ones that could be used to save her kingdom, which is on the verge of war, or destroy it.

Jessica Day George makes a memorable debut in this enchanting tale of dragons, betrayals, and the power of friendship.
Reviews "Clever, well-plotted and good fun."- Kirkus Reviews "[T]he fairy-tale action and vivid scenes, from glittering dragon cave to posh dress shop, are captivating, and readers will easily connect with brave Creel, who weathers betrayals and learns to value true friends and her own talents."-Booklist "First-time author George has created an endearing fantasy with quirky twists on traditional elements. ...The tale is told deftly and with warm humor, and readers will bond quickly with sensible country girl Creel. Romance, friendship, and betrayal all spice the mix, and readers looking for something to follow Hale's Princess Academy will find pleasure here."- The Bulletin of the Center for Children's Books "A magical, fun-filled page-turner for middle-grade readers that's a far cry from an old-school Cinderella story."-Bookpage "This is a light-hearted fantasy tale at its best."- MeridianMagazine.com