"We was slashing tires together. We were walking along poking them," said Gaines, 29, who pleaded guilty in November and was sentenced in January to 11 1/2 to 23 months in jail and 30 years' probation for slashing tires on 56 cars.
He testified against Lewis as part of a plea deal.
But Cunningham believed most of what Lewis had said.
He found her guilty of possession of an instrument of crime, conspiracy and criminal mischief for slashing one tire.
Lewis is free on bail and will be sentenced Sept. 10, Assistant District Attorney Allison Pavero said.
Lewis recalled an eventful night on Jan. 6, 2013, that included herself, Gaines and her boyfriend stopping at two West Philly bars, the second of which, she said, was held up at gunpoint and all the patrons forced to lie on the floor.
But when a drunken Gaines started slashing tires, Lewis said, she told him, "You're doing something stupid" and started to walk away.
Gaines continued to slash tires, Lewis testified.
"He's a grown man, he had a knife. He could have slashed me. I'm not the police," Lewis said when her attorney, William Montoya, asked why she didn't try to stop him.
Lewis turned herself in to police after surveillance video was shown on TV.