Bernadette Njoki Gachinga, 33, was adopted by Esther Wangari Kanuri at the age of three months after being dumped by her biological mother.
But on the evening of February 23, 2014, Ms Kanuri was brutally killed by unknown assailants at her home in Kihuyo village, Nyeri Town.
The slain civil servant's body was found by her husband, Michael Kanuri, lying in a pool of blood in her adopted daughter's bedroom.
Ms Njoki turned out to be the prime suspect in the murder. It is alleged that she attacked her foster mother while she was taking tea in her living room and stabbed her more than 15 times in the neck, chest and stomach.
She allegedly later dragged the body to her bedroom, locked it from the outside and escaped to Nyeri Town.
Ms Kanuri, who was suffering from arthritis, had just arrived home from a church service at Kihuyo Presbyterian Church of East Africa.
Although Ms Njoki has since denied killing her foster mother, the court found that she has a case to answer.
During her defence at the Nyeri High Court on Thursday, Ms Njoki admitted hating her foster mother. The court was told she made Ms Kanuri's life a living hell after discovering she was not her biological mother.
Justice Abigail Mshila heard that Ms Njoki was a wild and indisciplined girl since her days in high school and was addicted to drugs such as bhang and alcohol.
While being cross-examined by State Counsel Emma Gicheha and lawyer Gitonga Muthee for the deceased's family, Ms Njoki admitted that she became errant and defiant towards her foster mother after completing primary school education in 2001.
"I discovered that she was not my biological parent after snooping into a cabinet in the house that was always locked. I was 14 years then and I told my brother that we are adopted children.
"I became confused and escaped from home for one month to look for my biological mother but I later returned," Ms Njoki said.
She admitted harbouring a grudge against Ms Kanuri for reasons she did not disclose. She said she was not bitter although Ms Kanuri had not told her she was adopted.
Ms Njoki is accused of stabbing her foster mother to death following an altercation caused by her indiscipline.
The disagreement allegedly arose after Ms Kanuri asked her why she had not reported to her workplace in Nyeri Town where she was operating a fruits parlour.
The prosecution told the court Ms Njoki, while in high school, wrote a letter to her foster father telling him how she hated her foster mother.
"Remember I wrote to you an SMS telling you that I hate mum. I was angry. I wish I got to know my real mother," the letter reads.
The court heard that the accused had, at some point, attempted to commit suicide saying her foster parents had abandoned her.
The prosecution further told the court that two days before committing the murder, Ms Njoki had sent her pastor, Mr George Gichure Mwangi, a text message saying she was angry and would kill someone.
"I now prefer having the devil I know than a fake angel ... ungrateful parents ... I will make my parents' life hell on earth. The demons in me are furious and uncontrollable ... I will kill anyone who crosses my path," the message reads.
Ms Njoki, however, denies sending the message. On his part, Mr Kanuri testified that on the fateful day he went to his farm, leaving his wife and granddaughter at home.
Upon returning to the house, he found his wife lying in a pool of blood in Ms Njoki's bedroom.
"The bedroom's door was locked and the father had to break it. The accused was not at home. She surrendered at Nyeri Central police station and was arrested," the prosecution said.
But Ms Njoki denied surrendering to police. She said she learned about her mother's death through the media while at a pub in Majengo slums at around 4pm that day.
"While I was in the pub, four men came in and said they were looking for the woman who killed her mother. I went behind the club and started smoking bhang.
Later, at around 7pm, I left for Nyeri Town and saw some three men following me. I escaped and ran to the police station," Ms Njoki, a mother of one, said.
But the prosecution asked her why she never went home upon learning of her mother's death through the media.
"The accused continued drinking alcohol despite getting the shocking news. She did not call anybody back home to confirm the report. She was never bothered," Ms Gicheha said.
According to the State counsel, Ms Njoki had a frosty relationship with Ms Kanuri but was sympathetic to her father.
But Ms Njoki insists she loved her adoptive mother. She produced letters she sent to her parents when she was at Narumoru Girls, Kiriani Girls and Nyahururu Elites Senior School in which she described her love for them.
Hearing continues on March 27.