Raedburh

   Another name for Raedburh was Redburga.

  General Notes:

She was a Frankish princess, probably a sister or sister-in-law to Charlemagne.

This comes from Wikipedia

Redburga or Raedburh was the wife of king Egbert of Wessex and may have been the sister-in-law of Charlemagne as the sister of his fourth wife, Luitgarde ; other sources describe her as his sister (although Charlemagne's only sister was named Gisela) or his great-granddaughter (which would be difficult to accomplish in the forty-six years after Charlemagne's birth) or the daughter of his sister-in-law or his niece. Some genealogies identify her as the granddaughter of Pepin the Short and great-granddaughter of Charles Martel ; other scholars doubt that she existed at all, other than as a name in a much later manuscript.

She appears in a medieval manuscript from Oxford and is described as "regis Francorum sororia" which translates as "sister to the King of the Franks". More specifically, sororia means "pertaining to someone's sister", hence sister-in-law.

  Research Notes:

My information and source can be found at Foundation for Medieval Genealogy

Raedburh married Egbert , King of Wessex, son of Ealhmund , Under-King of Kent, circa 789. (Egbert , King of Wessex was born between 769 and 780, died in Jul 839 in Cornwall, England and was buried in The Old Minster at Winchester.)