If Wishes Were Horses — Anne McCaffrey

Young Tizra and her twin brother Tracell find their world abruptly changed when their father is unexpectedly called to fight in a war which promises to last much longer than the usual three-day skirmish. Their mother--the village healer--enlists her children to assist her in caring for the many refugees left wounded and homeless by the conflict. Inspired by her mother, Tizra learns never to surrender hope even in a time of fear and uncertainty.