Let me introduce you to Helia, a human (though her father was a dwarven lyrium smuggler) Crow specialised in Templar and Mage assassinations. She kidnapped Tishka, an Orlesian Human Tranquil to infiltrate the Montsimmar Circle for a contract. But instead of abandoning the Tranquil to take the fall on her behalf she decided the girl was worth keeping around.
Their alliance began a decade long series of assassinations in the Circle that made the Crow's career. Helia guided Tishka and taught her the way of the Assassin, knowing a Tranquil would never arouse suspicions. In a few years Tishka became a powerful Tranquil assassin, poisons, traps, wilderness survival, straight up stabbing, she became an expert in taking out Helia's targets before the Crow would whisk her away and reap the profits on their shared behalf. Helia also made use of Tishka's enchanting abilities by having the girl craft paralysing runes and enchanted traps. Some of Helia's closest friends at the Antivan Crows claim she was infatuated with the emotionless woman, some spread rumours that they even wed in a secret Crow ceremony.
Sadly, their alliance would come with the Fall of the Circles. Though Helia intended to keep Tishka under her thumb regardless of Circles to infiltrate, if only for her enchanting, a group of rogue Templars heard about this Tranquil living free of Chantry supervision and attempted to 'reclaim their property'. The fight was vicious and if the Templars did not live to take Tishka back into their custody neither did Helia.
Since then Tishka has vanished. Templars claim a Tranquil could never survive on her own, but the corpses of their brethren killed by traps and poisons, lured by the siren's song of a poor abandoned Tranquil woman, seem to prove them wrong.
Escaped Mages also claim to have seen the woman lurking in the Antivan wilderness but despite their offers to share the warmth of their fire she never joined, but in the morning they would find bundles of forage by their camp. These Mages also claim that as long as they remained in the forests they would find dead Templars but no live Chantry Knight would ever reach their encampments. Some have speculated she might have cured her Tranquility and have attempted to make contact to no avail. She became a known Apostate Legend in Antiva but none of these people ever knew her name not the name of the shadow of a Crow, riding on her shoulder.