I think this is quite likely to have been the mother of Osbeorn, Bulax
*If the story of Osbjorn's death as a boy at the hand of Macbeth in 1054 is true, then Osbjorn is born c 1039
*For Ælflæd (Siward's 2nd wife) to be his mother, she must be married to Siward Biornsson, Earl of Northumbria in c1038 at 18 - which puts her birth date at c 1020.
*This makes Aeflaed’s father - Ealdred, Earl of Northumbria & Bernicia 's age at her birth, only about 14yrs - given the likely date for his parents’ divorce as c 1007.
All possible; especially as based on so many estimated dates – but close enough to make a good case for Osbjorn’s being a child of Siward’s first marriage, to Godgifu of Northumbria Godgifu.