No, according to the news stories I posted, they could be rapists, robbers, and murderers. But you're going to just ignore all that. Old people are frail. Why would you answer the door armed? Maybe because in your affluent neighborhood, random strangers just don't normally come a knockin'. And when they do, it might spell trouble. And a firearm evens out the odds a little. Answering the door with a gun may make someone an asshole, but it's not a crime to possess a gun in your own home (felony status notwithstanding).
I'm not arguing that she made a mistake drawing on the officers. If she could see they were cops, she should have dialed 911 to get whatever happened to her on tape and complied with the officers' wishes. And maybe tossed a dog at them to shoot so they could still get their rocks off.