A lot of people with depression or bipolar disorder tend to try to self-medicate with drugs, sex, or alcohol. Even if this Corey kid was using, *if* his mother was failing to get him in to see a psychiatrist and keep him on appropriate psychiatric medication for whatever it was he had, I would blame the parent for negligence in taking him in for necessary medical treatment.
*If*, OTOH, mom was doing her level best to get him to psychiatric appointments and try to keep him on whatever meds the doctor prescribed for his mental problems and they just couldn't get his meds right, or couldn't get him to stop using illicit drugs, or he wasn't responding well to the psychiatrist's best attempts to properly treat his condition, then it wasn't the parent's fault, it was just one of those terrible tragedies.
You can't save everybody, unfortunately.
Whether the mother is to blame or not, as far as I'm concerned, boils down to that---whether there was or wasn't negligence in getting the child necessary medical care.
The parents who try to kid themselves that their seriously mentally ill child can be treated with prayer and discipline, or love, or citrus, or vitamins, or whatever their favorite alternative treatment is are every bit as bad as the Scientologists who will let their kids die rather than have a diptheria shot or a blood transfusion.
But with the major mental illnesses, not every patient responds well to medication, and sometimes you have tragedies no matter what you do.
Without more information, I've no idea which category Corey's death belongs in.