Since she died in West Virginia in 1973, my understanding is that you need to contact the West Virginia Health Statistics Center, which gives the following information about who may obtain copies:
"Certificates will only be issued to the next of kin or to persons with a legal right to the certificate. If you have questions concerning the right to obtain a copy of a death certificate, please contact the Vital Registration Program at (304) 558-2931."
I haven't tried getting copies from them, and don't know whether being a greatgrandchild gives you a 'legal right'.