Since you have a full name and date of death in Queensland you can obtain information on the location and cause of death from the Death Certificate filed with the Registrar.
Details are in the Certificate Access Policy.
In short, you need to
- find a direct descendant (eligible on Family grounds now), or
- wait for another 10 years (when it becomes an historical record).
Otherwise, you need to look for other forms of evidence. Does anything on the headstone help you in identifying the undertaker?
There appear to be two monumental masons working in the area (Zeigler and Allen). You can obtain their contact details through the Bundaberg Regional Council website.