I don't think the surveyors do a title search for location surveys.  I know they do some initial research to find their beginning points and legal descriptions, but I don't think they do enough to discover easements.  I think the only easements they would show on a location survey would be ones that are visible on inspection of the property.  And, had this easement been visible, the owner/builder probably would have noticed.

How 'bout an alternate theory of extinguishment by estoppel.  If the easement wasn't regularly used and the easement owner watched the neighbor constructing a building on the easement property, the easement holder may be estopped from asserting her rights if doing so would cause unreasonable harm to the owner/builder.

Best,
Robert A. Franco
SOURCE OF TITLE