That's right. She was called "Madame Antoine" in Vienna. But she would not keep this nam in France, as a queen. Maybe... her most intimate friends still called her "Antoine", reminding her of her so sweet childhood... ?

I can't find any address for the author of Marie Therese- Susan Nagel. Though she did say,"It was here that the Queen , exhausted from the etiquette of the French court, banished curtsying and insisted that she be called by her first name."
It just seems more likely that if she wanted to be addressed informally she would have asked to be called Madame Antoine/ette.

Yes, seeing as all her sisters and m any relatives were named Marie, I can see why this practice would be needed. Even though we can never know 100%, I think you are correct in judging by what was custom.
As much as she came to love France, It also seems that she was perpetually homesick, so it would make sense if she wanted to go by Madame Antoine.
I think either way we can feel comfortable that in private she was addressed as either Madame Antoine or Antoinette. Could depend on where the visitor was coming from too. Austria vs France.

Her official signature was I believe Marie Antoinette d' France--the necklace affair paperwork used the wrong signature which was one reason it was found to be false. But to tell you the truth even the King and Queen addressed each other as Sire and Madame so how are we to know?

Jeanne de la Motte used "Marie Antoinette de France" and this was wrong- she didn't know Antoinette's signature contained only her name. Look, her ignorance and especially -idiocy- issued in the process on the Diamond necklace! What a shame

I couldn't have said it better

reine

As Fraser underlined it, it might not have been that obvious for someone that does not belong to the High Nobilty, but Rohan should have known. But that kind of detail mustn't be very striking when you're ecstatic about recieving a letter from the queen, after such a long disfavour. What I find fascinating about this affair, is that it all leans on the protaginists' psychologies.

As for her name, I really wonder if MA's close friends ever called her by her name, that is to say, Antoinette. Calling her Madame was already casual enough, since she was to be called Majesty. I know that Louis XVI did allow his brothers not to use the official title, when they should have done so. I have not read the queen's letters, I wonder how familiar she was to her friends.