Naiatli is an actor and understudy of Livius, who appears in the Death on the Isle quest. She's ultimately apprehended after being identified as the murderer, but only after the player survives intense on-stage combat.
The player will always deal a set amount of damage to her with each attack during the play, however the hitsplats are tinted darkly as if they did not come from the player, and do not award any combat experience.