In NewSearch when searching from your tree you can edit search to be sure you are searching for married surname exactly as spelled on findagrave, make it exact, and for a death year exactly as on findagrave, making that exact. You can specify searching for birth, marriage, death only.
That being said, Ancestry.com has not uploaded every listing indexed on findagrave.
Even if you get the Ancestry.com search engine to find the findagrave item you are aware of, when you go to save the citation to your tree the Ancestry.com software will not create a burial item. You must create the burial item yourself, then you can edit the findagrave.com citation to attach it to that event.