The unreliable narrator as victim
Most unreliable narrators in fiction are unreliable because of their own limitations: self-deception, limited perspective, deliberate concealment. The gaslight fiction narrator is unreliable for a different reason: her perceptions and memories are being actively altered by an external agent. Writing this narrator requires holding two realities in view simultaneously — her experience of events and the events as they actually occurred — and finding the precise calibration between them that keeps the reader uncertain. The narrative voice should be coherent and intelligent; the protagonist's unreliability is not about her cognitive limitations but about the systematic distortion of the information she is receiving. The reader should be able to trust her account of her own emotional experience even while questioning her account of external events.