Use of the "de" in double surnames.

My wife was a Mexican citizen living in Mexico when I married her.  
Her maiden name was: Isaura Martinez Vallejo.  Martinez was her 
father's last name and Vallejo her mother's.   After we got married 
and she was processing her papers to become a legal resident, her 
name became: Isaura Martinez Vallejo de Gonzalez.  The part "de 
Gonzalez" was added to designate her marriage to a "Gonzalez" That 
is how her name appears on her Green Card and also on her Mexican 
Passport. Once in the United States, she only uses Isaura Gonzalez, 
and that is how it appears on her American Passport and all of her 
legal documents. She is a U.S. Citizen now. 

I lived in Mexico for 10 years and noticed that that was the costum 
( law ? very possible, since that is how it used on official 
documents ) "de" is used like Mrs. is used here.

I believe "de" was also used in a different way when it was part of 
a name of a MALE to designate his place of origin.  Rodrigo Diaz de 
Vivar, better known as "El Cid" was from the town of Vivar, just 
outside of Burgos, in Northern Spain.

Ajay: I hope I answered at least one half of your question. I am 
sure there is somebody in the group with more extensive knowledge on 
this subject.

John Gonzalez
Wildomar, CA.