Online court records say the charges against Diane Hill were dismissed last week at the request of Custer County prosecutors.
Hill and her daughter, 24-year-old Brittney Pryce, were charged with second-degree murder and felony child abuse following the November 2013 death of Noah. Investigators say the he died of a head injury suffered while in the care of Pryce and her mother.
Noah was a ward of the state, and Brittney Pryce and her husband were his guardians.
Brittney Pryce still faces charges in the death. Her next hearing is set for July 24.
Charges against Hill could possibly be refiled at a later date.