Oh no...he's baaack

My g-g-grandmother is driving me nuts, though she's long gone. DNA news leads me to think she may be the link to distant relatives and extending my documented tree. But she's a slippery one, so I humbly turn again to you mavens. I simply cannot establish her genesis. She's the Berte Marie Thorsdatter in the 1865 census with Arent Johnsen and three of their eventual eight children. It shows her estimated age at 35, and being from Stavanger. So I thought I was finally making some headway. But then I digitally leaf through the Stavanger ministerial books beginning in 1830, and find that Berte Maria in various spellings was a very popular name, and I am utterly incapable of deciphering the priests' scribblings to find a father named Thor. Have you any suggestions and/or shortcuts to get at my great-great granny so that she finally leaves me alone? As always, thank you.