Don't you just love how they are angels for everyone else except you?
Really, your not the only one. Ethan's great grandparents think he's an angel who can do no wrong - five minutes through my door and he's usually screaming at me cause I've said no! I can't remember if I read it in Tracy's books or somewhere else but I recall something saying that because they feel comfortable and secure with you, they feel safer letting out all their emotions etc, (ie temper, ignoring you) in your presence rather than someone elses. Which sounds nice and reasonable when you think about it but its a pain in the backside when you're trying to get them to do anything!
I would just keep being consistent when telling her not to do something. Keep using the gentle but firm tone of voice and she will eventually get it.
I don't really have any advice for the church problem, we aren't churchgoers ourselves. Other than a small quiet toy or book to distract her I can't think of anything. Maybe someone else will have a better idea.
HTH