A narcissist and her lesbian lover have been convicted of killing a child after a campaign of abuse in which they donned fright masks to terrify the youngster.

Kiki Muddar, 43, and Polly Chowdhury, 35, terrorised Chowdhury's eight-year-old daughter Ayesha Ali for months, in Chadwell Heath, Essex.

She was found dead in her home in August 2013 after suffering a blow or blows to the head. Muddar and Chowdhury were in a relationship at the time which police described as "bizarre".

Muddar – who has borderline narcissistic disorder – concocted characters on Facebook to control Chowdhury, telling her in messages: "You have no right to ever love or like your evil daughter."

Ayesha was abused by the pair who wore horror masks to frighten her during the night. More than 50 injuries were found on her body following her death.

Chowdhury and Muddar held their heads in their hands as they were convicted of manslaughter at the Old Bailey.

Muddar refused to give evidence at her trial. Police said she used social media and messages to concoct a web of lies and deceit which influenced Chowdhury. Together the pair's behaviour toward Ayesha was "a picture of hatred," said Detective Sergeant Andy Nimmo.

"Ayesha Ali was an innocent and defenceless eight-year-old child caught up in a bizarre set of circumstances and manipulated by two adults who were intent on causing her harm.

"Through social media and text, Muddar created a sophisticated web of lies and deceit which took officers months to unpick. What unravelled was a picture of enormous hatred directed towards Ayesha by both Muddar and Chowdhury.

"Ayesha should have been able to turn to one person who she could trust - her mother - but Chowdhury had allowed herself to become influenced by Muddar and together they inflicted serious emotional and finally physical harm on Ayesha."

Ayesha's father attended every day of the trial. Afsar Ali, 35, said: "The reason why I wanted to attend every day was I wanted to re-live Ayesha's life, feel the pain. I don't think I can ever imagine what she had to go through."