You might tell her that you thought these were the best bet, because if you had put "Mrs. Cindy Lastname," it would have meant you were divorced. You can find documentation for that.
And that since you ARE separated, you thought it was disrespectful to your husband to put "Mrs. John Lastname," since he wasn't involved in anything inside the envelope. And that you really do want to be respectful to him.
And I agree, this is a great issue to take to your counselor to talk through this level of interference, and how to handle it, and how to not pay attention to it if you can't cut it off.