A KNIFE-WIELDING robber tried to bilk Sharon Doyle out of a hard day's pay at Stan's Health Food, her store on Frankford Avenue near Wellington Street in Mayfair, police said.

But he didn't realize that Doyle, 46, spent more than a decade working in law enforcement, including stints in the Philadelphia Police Department and the Secret Service. He also didn't know that he had brought a knife to a gunfight.

And he ended up in the morgue with a bullet in his chest from Doyle's .38-caliber revolver, according to police.

Her parents said it was the first time their daughter had to fire a gun outside of ballistics training.

"Someone was watching over her," Doyle's mom, Rita Perrello, said last night outside her daughter's store.

She noted, with a smile, that Doyle had gone to work that morning wearing her guardian-angel medallion.

It seemed to do the trick. Just after 5 p.m., the robber, 47, walked into the store, pointed the knife at Doyle, who was working alone at the time, and demanded money, Chief Inspector Scott Small said.

The bandit, who was known to police, walked behind the counter, picked up the cash register and smashed it on the floor, Small said.

As he stooped to pick up the scattered bills, Doyle reached for her revolver, which she first bought while working as a Philly cop.

When the robber stood up and pointed his 6-inch hunting knife at Doyle's chest, she opened fire, hitting him once in the chest at point-blank range, Small said.

When police arrived, they found the creep collapsed behind the counter, a $100 bill still clutched in his left fist. He was taken to Aria Health's Torresdale hospital, where he died of his injury about an hour later, Small said.

Doyle spent much of last night being interviewed by homicide detectives, but her dad, John Perrello, spoke with her just after the incident unfolded, and said his daughter was calm, despite what happened.

"I don't think it's hit her yet," Perrello said. "I think it'll come back to her tonight, while she's lying in bed.

"I know that's all I'll be thinking about before I fall asleep."

Perrello said his daughter first started working at Stan's as a part-time sales clerk about 15 years ago. She worked her way up the ranks, to the point that when the previous owner offered to sell the business to her, she jumped at the chance.

That was in 2001, and in the intervening years, Perrello said he was always a little concerned about his daughter operating a business in that area.

"It's not like she doesn't know how to handle herself, but you still worry, as a parent," he said. "I always was worried that I'd get a phone call about something happening at the store, that she'd be the victim.

"I never thought it'd happen like this, but, if it had to happen, I'm glad it was this way."