Jerika Trent, 23, pleaded guilty to the charge Monday. Her mother and co-defendant, Ella Reynolds-Huddleston, 45, pleaded guilty to robbery last week, a Lake County Sheriff's Department press release said.
Reynolds-Huddleston faces a maximum term of 53 years in prison after also pleading to three additional charges of fraud.
Members of murder victim Steven Allessio's family reportedly found Reynolds-Huddleston's purse behind his bed 17 days after the murder.
In the purse was a checkbook for an 82-year-old man who had cancer, and with whom Reynolds-Huddleston and her husband were living. Reynolds-Huddleston had forged her name on nine of the man's checks, cashed them and used his credit card, the sheriff's department said.
Authorities allege that on April 14, Trent and Reynolds-Huddleston had been smoking crack cocaine for three days with the 55-year-old Allessio, when the women decided to rob him of drugs and money. The victim was stabbed at least six times, including in the neck, stomach and abdomen, police said.