After the death of her brother Janusz III, a group of powerful nobles at the Masovian court attempted to maintain the separate legal status of Masovia and prevent its incorporation into the surrounding Kingdom of Poland.

In 1526 this group proclaimed Anna as Duchess, the last representative of the family (however, her elder sister Sophia was still alive at the time).

This resistance to the duchy's incorporation, which was largely caused by their fear of losing their significance, was also fuelled by political forces interested in maintaining the status of fiefdoms.

In this state Masovia would be united in resistance against the Crown and would also have encouraged the House of Habsburg (in comparison with the Polish rivalry for influence in Moldavia).

The dispute ended with the parliament in 1537, which forced Anna and her husband to take an oath before the king, and renounce the hereditary rights of Masovia and the estate for the benefit of the Crown.