In 1030, together with her husband, she donated the collegiate church of St. Blasius which was located immediately adjacent to the castle.
[4] In addition, Gertrud donated some altar equipment[5] which, as relics of the later cathedral, formed the basis of the Guelph treasure of future centuries.
[4] From then on, Gertrud took care of the education of their common, underage sons, trying to cultivate and strengthen the Brunonian family traditions.
When her grave was opened in 1668, fragments of a small lead tablet (7.5 × 10.5 cm),[9] which was probably part of an epitaph, were found in it, with the inscription: "Hic requiescit Gertrudis devota Christi famula.
[10] In 1173, Henry the Lion began the construction of the cathedral, probably in the same place where Gertrude's collegiate church, including her tomb, had been located until then.
[11] In 1935, the National Socialists exhumed the remains of Gertrude, Henry the Lion and his second wife Mathilde of England.