Someone has posted quite a few sources to your ancestor’s profile, so at the very least you should evaluate them all. At the time of her marriage, Elizabeth could not sign her name,so was clearly illiterate. Perhaps she learned later, or the census taker may have just made an assumption. If you have sources like census records for this family, you should add them to the profile(s). “Ancestry.com” is not a source by itself, you need to copy the iformation and link to the actual records. You may find some of the same records on FailySearch or other free sites.