[2] After the death of Peada, who was allegedly murdered with Alhflæd's connivance, and possibly Osthryth's as well, she retreated to Fladbury in Worcestershire, to judge both from the place-name, which means "stronghold of Flæde", and from its subsequent history:[3] sometime in the 690s Æthelred granted Fladbury to Oftfor, Bishop of Worcester, to re-establish monastic life there;[4] however, this grant was later contested by Æthelheard, son of Oshere, who maintained that Æthelred had no right to give Fladbury away, as it had been the property of Osthryth.
It is clear from this story that Osthryth played a part in promoting the cult of St Oswald.
Bede tells us that he was "a young man of about eighteen years of age and much beloved in both kingdoms, for King Æthelred had married his sister.
[9] Ann Williams attributes it to the hostility between the Mercians and the Northumbrians,[10] while D. P. Kirby suggests that it may have been revenge for her sister's alleged involvement in Peada's murder.
[11] H. P. R. Finberg speculates that she and her kinsman Oshere were suspected of trying to detach the kingdom of the Hwicce from Mercian overlordship.