So sorry. Your mother's letter was a complete watchtower manipulation with all the usual rhetoric. She wants you to come back into line and is concerned about your not spending time with them. She blames other people for the distance between you but fails to appreciate that it is her religion and the rules she is enforcing that cause the distance. If you were allowed to be true to yourself and she was allowed to accept that you have an alternative viewpoint then there would be no conflict. It is precisely because they are trying to enforce a paradigm where everyone has to believe the same thing that there is a problem.
In a normal family you accept that others have a different perspective and you may not agree with it but you love them just the same. You can still visit and be assured of acceptance since love isn't conditional on belonging to a specific religion or viewpoint. She is incapable at the moment of considering another perspective.