Sisters Of Sword And Song By Rebecca Ross

a thrilling YA stand-alone fantasy about the unbreakable bond between sisters. 
After eight long years, Evadne will finally be reunited with her older sister, Halcyon, who has been proudly serving in the queen’s army. But when Halcyon appears earlier than expected, Eva knows something has gone terribly wrong. Halcyon is on the run, hunted by her commander and charged with murder.
Though Halcyon’s life is spared during her trial, the punishment is heavy. And when Eva volunteers to serve part of Halcyon’s sentence, she’s determined to find out exactly what happened. But as Eva begins her sentence, she quickly learns that there are fates much worse than death.