Cecilia's brothers were the reigning Electors of Brandenburg, first Frederick II and later Albrecht III Achilles.
The marriage had been arranged by Emperor Sigsmund, like that of her sister Magdalena with Duke Frederick II of Brunswick-Lüneburg.
William and his brother Henry II had promised Cecila as jointure Bodenteich Castle plus an annual pension of 2000 guilders.
Bishop Magnus of Saxe-Lauenburg tried to redeem pledges to Duke Henry II, and in particular Wolfenbüttel Castle.
Cecilia was quoted as saying: this is not what your brother had in mind, and is behaviour unbecoming a Lord of Brunswick, even if I'd been only the wife of a lowly subject.