How do you address the Rebetzin? “Mrs.?” “Rebetzin?”
We used to go to one shule where I used “Mrs.,” and I guess she was fine with that. (At least, she never corrected me or asked me to change.)
We also attended a different shule; when I used “Mrs.” she asked me to call her by her first name. I wasn’t comfortable doing that, and I told her, but she insisted. (The Rebetzins in both cases were younger than me.)