Dallace, I don't think you understood my comment. I referred only to the data on the single 1940 census page, as shown on Ancestry, not "every page." Except for the naturalized citizens, every person on that census page shows as 'American Citizen Born Abroad,' right next to where it says they were born in Ohio. In your question you said, "I have only seen this in hers so far and no one else's." By "I added them," do you mean to say you corrected the Ancestry records to make them all say that? Regardless, I was only trying to help by confirming it as an Ancestry error, and I don't think I gave any cause for your tone.
ETA Thank you, Rick.