[2] A tradition related by the 13th century Vitae duorum Offarum tells that she was of Frankish origin, and that for her crimes she was condemned by Charlemagne's justice system to be set adrift at sea in an open boat.

Offa would fall in love with and marry her, at which point she adopted the name Quindrida, but she continued in her iniquitous ways before being murdered by robbers.

[5] In a letter to Cynethryth and Offa's son Ecgfrith, Alcuin advises him to follow the example of his parents, including his mother's piety.

[8] It has been suggested that Cynethryth's coinage was in emulation of the Byzantine Empress Irene, who ruled during this time through her son Constantine VI.

Some later chroniclers, such as Roger of Wendover, have alleged that Cynethryth was either personally responsible for the assassination of Æthelberht, or to have incited Offa to kill him.

[11][12] Cynethryth was alive as late as 798, when a dispute over church lands with Æthelhard, Archbishop of Canterbury, was settled at the Synod of Clofesho, at an uncertain location.