I think in the main series the full name is never given, it's just mentioned in the Guide and in SaSG. However, contrary to the Guide, RJ wrote SaSG himself and IIRC after the Guide. Thus I would say this rather indicates that the name in SaSG is the correct one. I also rather doubt that there are two Queens Ethenielle from different Houses, since RJ obviously wanted to imply that this text is more or less contemporary to the time of the main books.