So sorry for your dilemma.
It does sound like you have a good marriage in many ways and I'm happy to hear you are not seriously thinking of divorce. Hope the same is true of your thinking of suicide, you are not seriously considering it.
I notice you mention the Sister studying with your wife that she and her husband are a nice couple. That tells me you are a very balanced person. You have strong feelings against the Org, based on logic, research and study, but you can still recognize that their are nice people that are part of it. Focus on that because that is what your wife is seeing. She is going to church at the Kingdom Hall just like millions of people do in their respective religions. "The Truth" isn't as important as the social structure and her lifelong friends. I actually think that should be encouraging for you.
Don't panic or rush. Let her know how this is making you feel without accusing her of trying to be hurtful to you, just report how you "feel". I think you have a strong enough marriage that you will see good results from this.
Our goal in life should not be to change one another but to love one another.
I hope the best for you and your wife. Sorry to hear of the death of her mother.