The Silver Siren by Chanda Hahn

Every journey has an end.
Unable to find the answers she sought in Skyfell, Thalia, Joss, and Kael travel to Haven with a prisoner in tow. An attack on the road waylays their plans, and Thalia finds herself traveling alone with Kael to the hidden sanctuary of the SwordBrothers.
But war is on the horizon and the Raven is amassing his army. This time, the target is not Calandry, but the Sirens of Sinnedor. When family ties are revealed, Thalia must choose sides.
Desperate to break the final seal on her power and save those she loves, will Thalia willingly taste the bitter pain of the iron butterfly machine one final time?