Agreed! This problem would benefit from the input of a third party.

I would imagine that the sister would agree that prayer is hard work. Listening to someone pray in your ear when you'd rather they didn't is also hard work. It's completely understandable that the LW has other things she'd like to be doing with her energy. And that's just if we assume everyone is acting in good faith, rather than assume what I assume, which is that the sister is using the LW to feel important and gain position in her community.