From her brothers, Albert and Otto died young and the eldest, Herman, inherited the whole paternal domains.
The other two sisters are Kunigunde, who died unmarried, and Judith, married in 1303 with Rudolf I, Duke of Saxe-Wittenberg.
To that end, he decided to enter in an alliance with the Margraves of Brandenburg, cemented with the betrothal between him and Beatrice, who took in the city of Spandau on 19 April 1279; however, because of the close relationship between the groom and bride, the formal wedding was performed more than five years later, on 4 October 1284 in the city of Berlin (although the Papal dispensation to allow the wedding was announced one year later, in 1285).
Bolko I was succeeded by his sons, but because they were minors at that time, Beatrice's brother Herman, Margrave of Brandenburg-Salzwedel assumed the regency of his domains and the guardianship of her children.
The custody of Henry V the Fat's sons and the regency of his lands were taken by King Wenceslaus II of Bohemia.