French transcription of her name is Wilhelmine Catherine Frédérique Biron, Czech Kateřina Frederika Vilhelmína princezna Kuronská.

[citation needed] The secret relationship with a much older and married Armfelt resulted in the birth of an illegitimate daughter named Adelaide Gustava Aspasia (nicknamed Vava), who was born in secrecy in Hamburg on 13 January 1801.

[citation needed] Although Wilhelmine first met Prince Klemens Wenzel von Metternich (1773–1859) in 1801, their love affair did not start until the spring of 1813.

These letters also describe the minute details of the political situation of the day and the corresponding decisions made by Metternich as a diplomat and government official.

Modern historians speculate that Wilhelmine, who hated Napoleon, was the one who pushed Metternich away from a cautious pro-French position.

The negotiations in 1813 that resulted in an anti-Napoleonic coalition between Prussia, Austria and Russia were held in one of Wilhelmine's homes, Ratibořice Castle.

During the Congress of Vienna (1814–15), the relationship ended, as Wilhelmine didn't like playing the role of an unacknowledged mistress, a role forced onto her as Metternich was married, and also because Alfred Windischgraetz (alternative spelling) appeared in Vienna, and she could not resist resuming her affair with him, writing "with friends one counts the days, with you I count the nights, and I would not wish to miss a single one of them".

Because of her unknown origin (even the date of her birth is disputed) and the favour shown her by the duchess, several historians believe that Němcová could have been an illegitimate daughter of Wilhelmine and either Metternich, Count Karel Clam-Martinic or Windischgrätz.