Most likely, the female Killer Klowns prefer to stay back at home and are not as fascinated as hunting down humans for food like the ones seen attacking the town's population during the movie.
Mutated Human Women?
It is possible that these two Klowns were originally human women that the Killer Klowns captured and who have been turned into female Killer Klowns. The scene where Slim encased Debbie inside a balloon was possible foreshadowing to the fact that some female victims were not killed, but brought into the Big Top to be turned into Killer Klowns. One theory is based on the fact that Rich and Paul were kissed wildly by the female Killer Klowns, implying that they wanted to be impregnated to reproduce Killer Klown Offspring (And/or the male Killer Klowns were creating sex slaves.)
Interestingly, unlike the Male Killer Klowns, they seemed to have no interest in harming humans. Perhaps they were less violent, or just wanted men.