If you have no identifiable DNA matches that you can link into your tree at Great Grandparent level or beyond them then I would question that the lines you have may not be biological.
Well, quite! But we have DNA matches to her husband’s mother’s family, so know she is my great-granny. None of the rest of her more recent family has tested (or will test) except one, who discovered she was adopted as a result.
But even if somewhere there is a cuckoo in the nest, at that level there should be some matches, even if they’re not known to us. And there are no matches! Nothing at all that’s identifiable as relating to that line. All my closest matches are known or we can see exactly who they are. Most of them are from my mother’s family, but enough from my father’s other lines to confirm they are correct. I uploaded to several other sites with the same result.
She was from Oxfordshire, nowhere near the rest of my father’s family (Cheshire, North Wales, London). I do have groups of small matches that I can’t work out where they fit, but none of them seem to be from Oxfordshire.
Great-granny’s don’t drop out of a clear blue sky, but mine appears to have. We have baptism and marriage certs, but crucially no birth certificate. I think she was adopted, but records in the 1850s were none existent. But even adopted there should be something!