Undersheriff Estelle Reyes-Guzman can't help but feel that the recent beating of Carmen Acosta and the disappearance of Carmen's neighbor, Kevin Ziegler, are related. She's just not sure how. There had been a fight-over a boy. Carmen Acosta had been suspended for six days, Deena for only three. And Carmen's vengeful friends were still around. To most people, hat pins are vestiges of the past, used now only by elderly ladies who don't leave home without a hat. But Deena wanted something to defend