Sethstarkaddersmum: To answer your question, I am not familiar with any female massacres. ( I assume that's the answer you're after?) That's hardly surprising, surely? In general, women don't go around killing other people. I think we're all agreed on that one.
On the other hand, how many massacres/shootings are like the Poly, where all the victims were women? I know of no other case and if other examples exist, they must surely be rare. So this is/was a fairly unique situation, involving one very crazy individual.