LOL… this brings back some really weird memories which I wil not bring up as I’ve got friends on the CR who do not know who I am and I’d like it to stay that way :).
Personally, I think a rebbetzin is what you choose to become. If you’re the “rebbetzin type” and you do “rebbetzin stuff”—eg: helping people, being an awesome person, etc— then you can be a rebbetzin no matter who you’re married to and whether or not you’re married at all.
My aunt is a “rebbetzin bas rebbetzin” and she said that when my uncle first got his position in his shul, they were still “Rabbi and Mrs.” and now she’s grown to become “Rabbi and Rebbetzin” because it doesn’t come automatically.