It is a good letter, though I would drop the reference to Jehovah as a bogeyman. I also like Merfi's idea, make a point that if she was concerned about your daugther rather than trying to indoctrinate her they should come and visit you all.
It is a good idea to discuss the hypocrisy of the invitation with your daughter. That way when these approaches are made to your daughter she will become annoyed by it, rather than possibly confused.