To clarify the conflict of interest:
Michael said Terri wanted to die, and he hired a lawyer to get permission to kill her.
Terri's parents said Terri wanted to live, and they hired a lawyer in order to prevent Michael from killing her.
Who represented Terri? The GAL was appointed to make sure her rights were protected, and Florida law allowed, but did not require, the GAL to recommend that independent counsel be appointed for her. Please note that by "appointed" the law doesn't mean "paid for by the government." She had plenty of money for her own lawyer.
That's not what I was looking for. The presumption, I believe, is that one's legal guardian is acting in one's best interests. Under what circumstances is that presumption overturned, and outside representation required - aside from the obvious conflict of interest, that is.