From reading various sites on the web these hornets do raid honey bee hives.... However, maybe this was the queen -
New queens prepare nest sites in the spring, usually during April and May. The new queen builds a paper comb, lays a small number of eggs, and rears the first generation of offspring herself. This first generation develops into non-reproductive females (workers) that are responsible for defending and enlarging the nest and feeding and grooming the developing offspring.
Since it is only April I can only hope that this was a queen looking for a good nesting site or looking for food for her eggs. Anyway, I'm glad she killed it..... I'm going to have to become like Cindi and star a war on hornets!