(Gresham, OR)  --  Washington County authorities believe they've stopped a prescription-fraud operation out of Gresham.  Deputies have arrested 20-year-old Sirenna Lynn Guice and say they've seized medicine that has a 15-thousand-dollar value on the black market.  Investigators followed up on a call Saturday morning from a Gresham Walgreens, who reported a potential case of prescription fraud involving promethazine with codeine.  Detectives believe Guice is responsible for prescription fraud at multiple pharmacy locations.