Sorry not back to this sooner, I don’t think I saw it.
My great great great grandfather William Swearingen (b. Virginia abt. 1838,) was married to Susan Baker (b. Ohio abt. 1800). Baker is on her death certificate, and the informant was her husband.
In the 1870 census William and Susan Swearingen and children are listed in Dayton, Webster Co., Iowa. Daughter O.A. Swearingen was born in Ohio and was 8, which would make her 30 years old in 1892, in line with the marriage record you have.
By 1880 O.A. Swearingen is no longer in the household, which is not surprising at about age 18.
The sister I descend from didn’t use the same first name consistently, either, so that wouldn’t surprise me.