These vamp chicks aren't very smart. Based on their dispositions, they don't have the intelligence to cover their tracks, especially if they are allowing their meal to bleed all over the place; bang, forensic evidence they can place a vic on-site. Secondly, if they aren't careful, whose to say she won't turn into a vampire after being infected, then they have a new rival on their hands with full memory of having been betrayed. Third, do you know how difficult it is to get bloodstains out of something? Unless these vamp girls are able to snap their fingers and make entire bloody bodies disappear, they are going to have a fuck of a time explaining this to the club. Even if they use napkins or bleach to "clean up" their lips and mess post-feeding, that's still evidence that something happened in the back rooms. I mean, points for being sexy and all, but this sort of carelessness is what caused the first inquisition. These girls really need to learn the rules of the night, and the masquerade.