"I've gotten her to end contact with the OM."

This is where the problem is. She didn't cut it off voluntarily. She did it because you got the person in charge involved. Now see it from her POV. Does it make you seem like a hero or an @$$?

Establishing the boundary means that you set it and then don't actively do anything to make sure she sticks to it. It has to be HER CHOICE. And not because you exposed it to the music director.

Now if you told her that if she continued to see the OM, you would tell his W and everyone else in the church about them, then that's setting a boundary and what you did would have been justified because you established that as your boundary.

M-43 W-40
2D - 9 and 5

Emotion, yet peace.
Ignorance, yet knowledge.
Passion, yet serenity.
Chaos, yet harmony.
Death, yet a new life.

RECONCILED AND WISER