i think maybe staying away from church for a while might be a good idea.......for your benefit and nobody elses though.
speaking from experience sooner or later people like this always show their true colours, its just she has always had you to treat this way. if you withdraw totally from ANY contact whatsoever with her she will have to go and find somebody else to fulfill the role you have played in her life.
its not easy to walk away from a situation like this. when dp and i had a similar problem we totally withdrew from every person involved, directly or indirectly, and decided to rise above it (boy was it hard to keep my mouth shut!!). miraculously we still managed to be causing trouble for the person concerned even when we could prove we hadn't done the things we were accused of.
the hardest part was down the line seeing people i cared about being treated awfully by this person, and then the sudden realisation by everyone that i had been telling the truth all along. these were people who had known me and my partner for 10 years or more, i thought they knew me better but they were completely taken in by this person.
i am so sorry that you are caught up in such a bad situation.......but if you have the strength to do so leave her and her family to it. as i said sooner or later she will latch onto someone else and the nature of the beast is that the real her will come through.
i am thinking of you and will follow this with interest.