Faustina Collari
"Born and raised in a world of poverty, the Thief was taught how to steal, run and climb to survive, alongside her brother. Always together, acting as a team, they once split a pair of scissors to make a weapon, swearing to protect each other. It's been 10 years now... and she's never forgotten the day she broke her promise."
―Ubisoft description
Not very much is known about Faustina.
The Thief, as she is better known as, is an unlockable player persona. She unlocks at level 25, and she uses a Scissor Blade as her primary weapon.
She is not confirmed to be a Templar, as she doesn't appear in Assassin's Creed: Project Legacy or Assassin's Creed: Brotherhood Singleplayer. She is the only multiplayer character in Brotherhood that isn't in Project Legacy or Singleplayer.
According to Ubisoft's multiplayer description, she had a brother, who she neglected to protect, and in result, died.