People can put her on ignore, which could take care of option 3.
Other than that, the Elders can't remove from her the options to stir the peasants or auto da fe. However, doesn't that make sense? If someone comes in an illiterate village dressed as a SA priest and speak of the Bloodstars in a semi-cogent fashion, the peasants will just assume she's the real thing.
Realms can order her arrest. You can arrest all priests of realms you are at war with, even if they are of your own religion. Her own realm could ban her if they were so inclined (I don't think they are, but that's valid IC play).
I agree that a mechanism to boot a priest would be nice to have. However the situation is not so hopeless right now. There are things that all sides can do, if they're willing to do it.
I don't think her stirring up the peasants is really a problem. I'm pretty sure the most powerful stuff is Elder only and even if she can perform stuff like auto de fes, they can only be declared against non-SA members which limits their usefulness. The rest of the priest abilities, like stir unrest and badmouth realm, are so under powered that I doubt she'll even be noticed if there is not a priest nearby.
As for arresting- the only way that's going to be anything more than an inconvenience is if she's banned and executed, and the game is quite rightly designed so that that can't happen to you unless you deliberately take pretty silly risks.
I do think the whole can't excommunicate a priest thing is stupid, mainly for rp reasons, but the non-Elder priest game is so under powered that I don't think its game breaking.
