I think that perhaps the police might still be a trifle miffed that she called four of them "murderers" during the jury selection process of the Amadou Diallo trial -- even though they were soon acquitted, and by a jury in the Bronx. Not to mention the fact that the car she was in practically ran over a cop at the Westchester County Airport just mere days ago, and the officer had to go to the hospital, with no condolences from Her Highness.
They know that she has no respect for them and just views them as an occasionally good photo-op. Her feelings toward the military and uniformed people overall aren't exactly unknown.
And they also surely know that she's an elitist sow who thinks that an expensive education makes her a better person than those who do real, honest "dirty work."