Anna Jakobsdtr.

Christen is listed in his father's section of Etnesoga V to have had a child named Siri with Anna Jakobsdotter in 1740, but in Christen's own section there's no mention of either Jakobsdotter or Siri from 1740. Siri from 1740 were most likely born out of wedlock. Christen also had four other daughters named Siri later on.

Source: Etnesoga V page 156 Frette (mother of 25e.1).