I don't know if this is the case in Boyd, but sometimes branch libraries have neighborhood genealogy materials that aren't in the main buildings. I've found local funeral home/cemetery original records in such places, even plot maps and unique family history notes.

You've probably thought of this, but just in case: are there Sparks family who were close to her (parents, siblings) whose records you've found? Perhaps she was buried in the same cemetery as one of those. It's not unusual for surveys to miss a grave here and there, despite the best efforts of the volunteers who do them. Also, it's not terribly unusual for the DC to have an incorrect shipping location. The person who completed the DC may not have had complete info, or may have jotted the city he/she was most familiar with in the general area of the destination. Ashland may have provided the service needed for rail transfers, with the local funeral director to pick up from there. There didn't seem to be much inclination to update or correct records until after WWI. You might also try Lawrence County cemeteries.

Good luck!