I know this could be a veeeery long stretch, but could Barbara Nellie Lunsford case from 1963 be a possibility. She has an eerie resemblance. I dont know whether DNA could not have degraded to the extent of giving a false PMI as recent as 1990... what do you think?
The National Missing and Unidentified Persons System (NamUs)
The National Missing and Unidentified Persons System (NamUs)