If Allison gets excommunicated, will Astrum lead a fancy crusade to capture the heretic and place a nice pious priest in her stead? Methinks she'll be arrested before very long though. Local laws and what-have-you.
And what if she does? The could torture her, though that isn't likely to play well. The can keep her in prison for a while, then she can go right back to preaching where she wants. Unless she is caught trying to influence the peasants or incite stuff, its not like they can ban her.