Lady Knight by L-J Baker

Rhiannon, outcast and female knight, seeks a cause worthy of a chivalric hero in a medieval world of magic and misogyny. Eleanor, a wealthy widow, has given up all hope of finding passionate love and her perfect knight--until she meets Rhiannon. Aveline, a powerful priestess, needs a warrior for her secret mission of starting a holy war. She binds Rhiannon with double-edged oaths and a magical sword.

A love affair worthy of troubadours' songs clashes with loyalty, intrigue, ambition, and war, tangling the three women in a web that perhaps not even Rhiannon's sword can cut through.