Parker, 39, who represents the 200th Legislative District, which includes Mount Airy, Chestnut Hill and Roxborough, was arrested on DUI charges in the early-morning hours of April 30.
Two city police officers said that they stopped her state-owned SUV after they saw it going the wrong way down one-way Haines Street, in Germantown.
After hearing Parker and arresting officers Israel Miranda and Stephanie Allen testify during a September motion hearing, Hayden in November ruled that the officers lacked credibility and that the traffic stop was not lawful.
His ruling meant that all evidence from the stop was not admissible in court.
That evidence included the officers' testimony that Parker's eyes appeared glassy, that she smelled of alcohol, that her speech was slowed, that she was unsteady on her feet and that a Breathalyzer test measured her blood-alcohol level at 0.16 - twice the legal limit.
"We're back in the ballgame," a pleased state Senior Deputy Attorney General John J. Flannery Jr. said after leaving court.
"The other evidence - the Breathalyzer, etc. - will come in at the Municipal Court trial," said Flannery. "We'll be able to try this defendant."
His office is handling the case at the request of city District Attorney Seth Williams, a friend of Parker's.
"The Attorney General's Office decided to put Judge Hayden on trial here, which is a disgrace," Kelly said.
He said he would file an appeal to Superior Court by week's end.
"This is the worst testimony I've ever seen out of 15,000 DUI cases that I have done," Kelly added, speaking of the officers.
Kelly maintained that Parker had not driven the wrong way down Haines and that she and Hayden are not friends, despite the Facebook connection.