What was your greatgrandmother's name when she died? Do you have the exact death date and location in 1965? I probably won't be able to help you if they lived in Mexico up until 1930. I have no census for Mexico. If she died in the US in 1965 you can request her death record from the county where she died and it may state her parent's names. There may have also been an obit with family info in a local newspaper in the county where she died.
I hope you can get me more info. Her death records would probably be in the name of her last husband Petra ?. What was her 3rd husband's name?