Alien Conquest — Tracy St. John

An invasion has Cassidy fighting for her soul, but it's her heart Clan Tranis is determined to claim. Cassidy Hamilton doesn't think life can get any worse after being sequestered in a convent on Europa. A Kalquorian invasion quickly changes her mind, and she barely eludes her people's greatest enemy. Fear and desire become a heady mixture when her spying reveals the aliens' intentions for Europa's nunsbondage and seduction. But that's nothing compared with the plans Captain Tranis and his clanmates Lidon and Degorsk have for the young woman when they capture her.