No. This is entirely an issue of the state. Private citizens do not have these powers. Personal wishes have nothing to do with it.
The Legislature recognizes that for some the administration of life-prolonging medical procedures may result in only a precarious and burdensome existence. In order to ensure that the rights and intentions of a person may be respected even after he or she is no longer able to participate actively in decisions concerning himself or herself, and to encourage communication among such patient, his or her family, and his or her physician, the Legislature declares that the laws of this state recognize the right of a competent adult to make an advance directive instructing his or her physician to provide, withhold, or withdraw life-prolonging procedures, or to designate another to make the treatment decision for him or her in the event that such person should become incapacitated and unable to personally direct his or her medical care. § 765.102(3), Florida Statutes.
Why did Terri’s husband get to make the decision about whether she should live or die?
Michael Schiavo did not make the decision to discontinue life-prolonging measures for Terri. As Terri's husband, Michael has been her guardian and her surrogate decision-maker. By 1998, though -- eight years after the trauma that produced Terri's situation -- Michael and Terri's parents disagreed over the proper course for her.
Rather than make the decision himself(which he could have done thereby negating all the idiocy that followed), Michael followed a procedure permitted(key word being "permitted",...not "required") by Florida courts by which a surrogate such as Michael can petition a court, asking the court to act as the ward's surrogate and determine what the ward would decide to do. Michael did this, and based on statements Terri made to him and others, he took the position that Terri would not wish to continue life-prolonging measures. The Schindlers took the position that Terri would continue life-prolonging measures.
Under this procedure, the trial court becomes the surrogate decision-maker, and that is what happened in this case. The trial court in this case held a trial on the dispute. Both sides were given opportunities to present their views and the evidence supporting those views. Afterwords, the trial court determined that, even applying the "clear and convincing evidence" standard -- the highest burden of proof used in civil cases -- the evidence showed that Terri would not wish to continue life-prolonging measures.