Need help finding evidence of U.S. citizen parent's physical presence

[canadianmom]

My husband is Canadian (as am I) and wants to get his U.S. Citizenship through his mother. The problem we are running into is coming up with evidence of my mother-in-law's physical presence in the United States:

Evidence of U.S. citizen parent's physical presence in the United States before the child's birth, such as school transcripts (not certificate or diploma), university transcripts (not certificate or degree), employment records, social security record of earnings, other documentation that corroborate the Affidavit of Parentage and Physical Presence. The physical presence requirements set by the Nationality Act and the U.S. Immigration and Nationality Act (INA) are
Child's birth between December 24, 1952 and November 14, 1986, the requirement is ten years of physical presence in the United States by the American parent, five of which were after age fourteen, prior to the child's birth.

My mother-in-law stopped school in grade 9 (she was 16 by the time she stopped), and worked from age 16-17. Then she quit because she became pregnant with my husband's older sister. She then moved to Canada and got married on the same day (it was after her 19th birthday). So she is cutting it quite close. Besides school transcripts (which will only get me to age 16), I am in the midst of trying to track down information through Social Security. The year of earnings, and also the fact that her mother (my husband's grandmother) collected benefits while she was a minor. And she is pretty sure she collected benefits after she turned 18. She lived with her mother the entire time until she moved to Canada and got married (and has lived here since).

Does anyone have any other ideas on proving physical presence? I am not aware of how the government tracks everything since I am not an American and am not fully aware of how the system works.

[canadianmom]

My mother-in-law call the Social Security office closest to us and they looked up her social security number and were not able to find any records earnings. Probably because it was not a significant amount that needed filing. They also could not find anything about benefits being collected. My mother-in-law is going to look for her mother's social security number (her mother is deceased) and see if they can find any records via her mother's number showing perhaps that my mother-in-law lived there and had benefits collected while she was a minor.

I called the Census Bureau and they referred me to the National Processing Center to do a search. I left a message and am waiting for them to get back to me.

Any other ideas?