Helena, is an NPC that can be found in The Forest Encampment in Act 2. She is first encountered during the quest Intruders in Black in the The Chamber of Sins Level 2, hiding from Fidelitas, the Mourning, and needs to be saved.
Helena is an ex-Blackguard who, having witnessed Piety's insane ambition and cruelty while in her service, finally decides to turn against her after she is rescued from a horrible death at the hands of Fidelitas - after the rest of her unit had been massacred and Piety escaped, leaving Helena behind.
Once she is rescued and arrives in The Forest Encampment, there is obvious uncertainty as to whether she can be trusted. It is clear, however, that she is utterly disgusted and horrified by what she had seen, and zealously aids in thwarting Piety's plans with any knowledge she can provide. She also appears to be more than a simple soldier, possessing remarkable knowledge and intelligence.