What steps should I take to extend a Non O visa for my spouse related to our marriage certificate?

This is not really a thai VISA question but I'll let it on and then close commenting.

You are confusing BUYING a visa from a thai consulate in another country OUTSIDE Thailand with getting an extension of stay at the immigration office INSIDE Thailand.

Those things are done by two completely different governmental offices and have zero to do with each other

As an amercian you might notice that the US Embassy here does NOT certify marriage certificates because in the US you're not married by the federal gov't but by the state you're in.

BE that as it may there is a "work around" to getting it "certified" in a fashion. You go to the ACS (American Citizen Services) website of the US embassy in Bangkok, find the "blank affidavit" and fill that out that "AAA, born on, with passport number, was married to BBB, born on, with passport number, and the marriage certificate dated xxx from yyy state is real and accurate". The embassy WILL notarize that, then you take that to a translator, get it translated into thai, take it to the ministry of foreign affairs office and get that translation certified and THEN you can present the US marriage certificate to show proof of marriage so your spouse can get an extension that matches your entry stamp for 1900baht at your immigration office.