Rachel then got her mum to drop her to Anna's house in Morrison, Illinois and the teenagers proceeded to try to clean up the mess.
They went to sleep and the next day moved Peggy's body from the lounge to her bedroom, before covering her with a sheet, the Sun reports.
After realising they couldn't get rid of the evidence or body, the girls set the house on fire with the intention of using it to blame for Peggy's death.
Chillingly, Anna wrote a message to her mum on Facebook after her death.
“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,” she wrote.
”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.”
Upon going home, Rachel confessed to her mother what had happened and they proceeded to go to the police.
Anna was found at her father’s house and later confessed everything. She has been charged with two counts of first-degree murder, concealment of homicidal death and arson.
Rachel is yet to be charged. The pair will appear in court August 8th.