This makes no sense?

Question:My ancestor named Nichols (surname) came to the US from Italy.
On the 1900 US Census it said his wife was from Italy, then on the 1920 (or close to it, not for sure which it is) it said she was from Spain. We don't know her maiden name, only her married name. I found the one that said she was from Italy and my mom claims that she found the one that said Spain, all the other information checks out as the same except for the origin of Nichols' wife, again though I never seen the record she was talking about.

Best Answer - Chosen by Asker: My ancestor named Nichols (surname) came to the US from Italy.
On the 1900 US Census it said his wife was from Italy, then on the 1920 (or close to it, not for sure which it is) it said she was from Spain. We don't know her maiden name, only her married name. I found the one that said she was from Italy and my mom claims that she found the one that said Spain, all the other information checks out as the same except for the origin of Nichols' wife, again though I never seen the record she was talking about.

It only makes "no sense" if you are new to research. Most oldtimers know that conflicting information is normal, for a variety of reasons. Many times, the adult was not home when the census person came, and someone else.. child, neighbor, so forth.. gave what they believed the right info was. Ages varying is completely normal.
You have followed the advice to always get all documentation you can, right? Does her death certificate include the names of her parents? death certs for her children, should have her maiden name. 1900 should tell you the year she immigrated, would she have been single or married, at the time? You have estimated her marriage date from ages of children? looked for her marriage record in the county where she was 'first' located?
If you are fortunate, you may well find her and family in immigration listings on ancestry. And yes, you'll need that maiden name to do that. It should show their place of origin. Same for naturalization for her father, once you know who he is (assuming he lived and became a citizen).
Don't overlook the 1930 census, even if she already died. Adult children will list the birthplaces of parents, even if they don't specify mom's name. If you wind up with 10 records saying Spain, then Italy is probably the mistake (or vice versa).