According to KWQC news, firefighters were called to the house where they discovered the 53-year-old's body.
Rachel then allegedly confessed to her mother before heading to the police station.
According to reports, Anna posted a message on her dead mother's Facebook page, writing: "I don't even know if you can see me right now but if you can I just want you to know you were my best friend.
"I wasn't always the best daughter and I'm so sorry. I love you so much mum I just want you to know and I'll never forget you."
Anna broke down and admitted to killing her mother, police told a court.
Anna was charged with two counts of first degree murder, concealment of a homicidal death and arson. Rachel has not yet been charged.