The Annales Stadenses refers to the mother of "Ida [de Elsthorpe]" as "sororis Leonis papa qui et Bruno". The correctness of this parentage of the wife of Liudolf assumes (which appears likely to be correct...) that Ida von Elstorf was his daughter.
The Libro Memoriarum Sancti Blasii records the death in Jul 1077 of "Ghertrudis marchionissa senior". 1
Marriage Information:
Gertrud married Liudolf VON BRAUNSCHWEIG, Markgraf in Frisia, son of Gf. Bruno I VON BRAUNSCHWEIG and Gisele VON SCHWABEN, Duchess of Swabia. (Liudolf VON BRAUNSCHWEIG was born between 1003 and 1005 and died on 23 Apr 1038.)
Sources
1 Foundation for Medieval Genealogy, Medlands: Gertrud.
Research Notes: