10 January - St Sæthryth, O.S.B.

Another of the old Anglo-Saxon saints is commemorated today, St Sæthryth, 2d Abbess  of Faremoutier-en-Brie.

This site gives the following information:

Princess Saethrith was the daughter of  King Anna of East Anglia by his first wife of unknown name. Like her younger half-sisters, Sexburga, Etheldreda, Withburga and Ethelburga, she became a nun. This was after being educated with the latter by St. Fara at the nunnery in Faremoutier-en-Brie in France. She later succeeded her teacher as the second abbess there. She died on 10th January sometime in the late 7th century.

She's mentioned a few other places on the web but every mention is short and says not much more than that quoted above.  One site says she is mentioned by Bede the Venerable.   Another calls her the least known of the sisters.  True enough, so far as I can tell.  I had never heard of her to be sure.