Authorities say Gail Townsend-Finley failed to provide a safe environment for the child and left drugs where he could reach them.
Jamere Arnold, 8, died of cardiac arrest after taking Fentanyl at her home last summer.
Townsend-Finley initially gave police a cover story, telling them that her grandson ingested alcohol.
She is facing one count of involuntary manslaughter and one count of second degree child abuse.