I would just respond to that by agreeing with her....to a point. Sometimes clearing the air and confirming her fears can be a start to moving the discussion beyond whether you are a zealous JW or not.
For example you could say:
"I feel you think that the only way we can have a good marriage is if I am being a zealous Jehovah's Witness. I am sorry, but I don't think I can be the zealous Jehovah's Witness you think you need me to be right now. I have to say I do have some issues with the Watchtower.
But I do not have doubts about our marriage and I am committed to it and to being a good husband to you, just like the bible says husbands should be.The bible says that women should stay with their husbands, even if they are unbelievers, so that they may be won without a word. I am not an unbeliever, in that I do believe in Jesus (obviously only if you do), my only doubt is about some of the people in this organization, so I ask you to respect this advice from the bible, even if you find that hard to do, as I respect your right to believe in this man made organization.
If you will love and trust me, then we can have a strong marriage even if we do not agree on some things. "