A Montana woman accused of hiding the body of her 2-year-old son in the trunk of her car for most of last summer has pleaded guilty to negligent homicide and evidence tampering.

Summer Many White Horses appeared before a judge in Great Falls on Friday. The 31-year-old woman could be punished with up to 100 years in prison when she is sentenced next month in Cascade County District Court.

The Montana Department of Justice said her son, James, was last seen with her on July 21. His body was found in the car trunk on Sept. 5, after Many White Horses told Great Falls police the remains were there.

She originally was charged with deliberate homicide and evidence tampering.