I live alone and I'm not quite 92 but if I had people knocking at my door, IN PLAIN CLOTHES, yelling that they are cops, I wouldn't have let them in either. And I would have gone straight to my 12 gauge, loaded it... and waited.
That being said, I haven't done anything to deserve cops knocking at my door, which I would think this lady didn't either but who really knows.
Nothing against the cops... but I have as much right to protect myself as they do.