Sisters of Sigmar
They are all but extinct in the rest of the Empire with most of the remaining sisters having settled in the nunnery in Mordheim.
In the current day of canon, most of the original Sisters were wiped out with the chaos of the Mordheim events. However, they spread their faith throughout the Empire creating a large second generation of Sisters. They're independent of the church and thus differ greatly from convent to convent. Many rededicated themselves to other gods, like Morr. In addition, vampires from the Lahmian bloodline have infiltrated their numbers. Some were convinced that Undead aren't really heretical after all and use their immunity to disease to get into areas struck by plague and care for the dead and dying. Others are more in line with true vampires, using their disguise for political leverage while indulging themselves behind closed doors.
Because REAL women take the purging flame directly to the flesh of the heretic, and would never worship an Undead abomination who does not wield a hammer.