Okla. Stat. tit. 43A, § 43A-11-111
Petition for appointment of guardian
Any person may petition the district court for appointment of a
guardian for a declarant when the person has good reason to believe
that the provision of mental health treatment in a particular case:
1. Is contrary to the most recent expressed wishes of a
declarant who was capable at the time of expressing the wishes;
2. Is being proposed pursuant to an advance directive for
mental health treatment that has been falsified, forged, or coerced;
or
3. Is being considered without the benefit of a revocation
which has been unlawfully concealed, destroyed, altered or canceled.