I've got some Montgomeryshire records that might have Sarah Owens on if you've not followed her up. Some of my ancestors were from Montgomeryshire. Have you followed up Jane Evans? She intrigues me - is that a goitre ?
The majority of the census records for Sarah say b 1801, and the only Montgomeryshire baptism record I can find on IGI at that time gives parents as Richard Owen and Jane Tamberlain. Any light you can shine on this possibility or others would be great.
I've managed to get quite far with David, due to his occupation. He appears to have built a very successful cabinet making business in nearby Vaughan street. But for Jane I have not got anywhere, yet. Her parents lived alone in the 1871 census. She may have married. Or she may have died. There are, however, many Jane Evans's who got married in Llannelly between the census dates, whereas there are no matching deaths. So it would seem most likely that she got married. Evans is not an easy name for research, though, especially in Wales.
As for possible goitre? Hadn't noticed before, but now that you point it out.... hmm, maybe. If it is, at least it is only mild. I'm sure it would have been covered, otherwise. In the photograph, her clothing seems to accentuate her neck.
Wouldn't it be nice if we could just pop back in time and be a fly on the wall?