Vernita was Stone Cold
I was just bumping around a Kill Bill fansite and it pointed out that Vernita Green would be about three months pregnant at the time of the massacre at Two Pines. Imagine being pregnant, getting the word that you have to gun down your former friend and ally, and she's pregnant, and you kick her and shoot her anyway.
Vernita was pretty evil. Either that or she just really was ticked off that she couldn't be Black Mamba...