Dragon's Egg by Sarah L. Thomson

It is a rare talent, and only she can care for the Inn's herd. She feeds them, gathers their eggs, and tends to their injuries. But Mella dreams about the dragons of legend, even though hardly anyone believes they still exist. Dragons are small farm animals, not huge fire-breathing monsters. Everyone knows that.

Until one day changes everything.

A Knight of the Order of Defenders arrives at the Inn. Signs of the mythical dragons have led him there, he says. Then a simple errand takes Mella through the forest, where she stumbles across a dragon's egg—and faces the true, terrifying dragon guarding it. On the spot, Mella vows to get the egg safely to the fabled Hatching Grounds. She must leave her home for the first time, and she finds an unlikely companion in the Defender's squire, Roger.

For Mella and Roger, this one day is the beginning of an adventure. Where will it take them?