We are really reaching now aren't we? A subpoena is not some magic carpet that sweeps all before it. It is simply an order to appear, to which the guardian must respond. Nothing more, nothing less. Greer is not a party.
Greer is aparty, lol, though not summoned himself. He is interfering with the appearance of a subpoenaed witness, you dolt.
Terri can't respond if she's dead. Greer ordered her murder to begin. Witness tampering. Kind of like he put a hit out on her.