Leaving this for the next person who looks:
There seems to be two sisters of the same name here - one born 1846, one born 1848. Both lived long lives; at least one married and had children. In one record (this one's marriage), I think the other one's birthdate was used.
The other one is Britha Helgesd. Andersen
I found a large number of entries in Digitalarkivet, including church book images, that form the basis of my conclusion about the wrong birthdate. My notes on the chase are here:
https://wiki.geni.com/index.php/Britha_Helgesdatter_Thue
Enjoy!