[4] Mary's elder sister, the Baroness von Waechter, sent for her to live with her in Paris, where she met and later married Prince Frederick of Schleswig-Holstein-Sonderburg-Augustenburg on 3 November 1864.

Mary Lee, not wishing to enter into a morganatic marriage, induced the prince to renounce his rights and titles as a member of the royal house of Denmark.

[6] The princess then returned to Paris, where she resided with her sister, Baroness von Waechter, until the beginning of the Franco-Prussian War, when she accompanied the latter to Württemberg.

Empress Victoria envisioned an English-style constitutional monarchy, while Countess von Waldersee wanted "...the crown to rest on the head of a pious and socially concerned Christian ruler, but one who was also a politically conservative Pan-German nationalist in the Prussian rather than the English tradition.

"[11] She continued a pious life in Altona and Hannover, where her husband was appointed to, and supported the German branch of YMCA, founded by her friend Friedrich von Schlümbach, as well as other charitable organizations, like the Hamburg City Mission.