Question: What was the name of Archduchess Elisabeth Marie of Austria's father's mistress?

Context paragraphs:
Archduchess Elisabeth Marie of Austria: Archduchess Elisabeth Marie of Austria (Elisabeth Maria Henriette Stephanie Gisela; 2 September 1883 – 16 March 1963) was the only child of Rudolf, Crown Prince of Austria and Princess Stéphanie of Belgium, and a granddaughter of Emperor Franz Joseph I of Austria and King Leopold II of the Belgians.  She was known to the family as "Erzsi", a diminutive of her name in Hungarian.  Later nicknamed "The Red Archduchess", she was famous for becoming a socialist and a member of the Austrian Social Democratic Party.

Princess Stephanie of Windisch-Graetz: Princess Stéphanie of Windisch-Graetz (April 4, 1909 in Ploskovice, Bohemia – May 29, 2005 in Uccle, Belgium) was the daughter of Prince Otto Weriand of Windisch-Graetz (1873–1952) and Archduchess Elisabeth Marie of Austria (1883–1963), only child of Crown Prince Rudolf of Austria and Princess Stéphanie of Belgium.  She was the great-grandchild of Emperor Franz-Joseph and Empress Elisabeth ('Sissi') of Austria.  She was also the great-grandchild of King Leopold II of Belgium.

Stéphanie Windisch-Graetz: Stéphanie Windisch-Graetz (born 17 July 1939) is the daughter of Prince Franz Joseph zu Windisch-Graetz and granddaughter of Archduchess Elisabeth Marie of Austria.  Archduchess Elisabeth was the daughter of Rudolf, Crown Prince of Austria and granddaughter of Emperor Franz Joseph I of Austria.

Archduchess Elisabeth of Austria (1922–1993): Archduchess Elisabeth of Austria (31 May 1922 – 6 January 1993) was a member of the House of Habsburg-Lorraine.  She was the youngest daughter of Charles I, the last Emperor of Austria, and his wife Zita of Bourbon-Parma.

Archduchess Elisabeth Franziska of Austria: Archduchess Elisabeth Franziska Maria of Austria (17 January 1831 – 14 February 1903) was born in Ofen (Buda), Hungary, the daughter of Palatine Joseph of Hungary (1776–1847) and his third wife Maria Dorothea of Württemberg (1797–1855).

Archduchess Elisabeth Amalie of Austria: Archduchess Elisabeth Amalie of Austria (7 July 1878 – 13 March 1960) was a daughter of Archduke Karl Ludwig of Austria and his third wife Infanta Maria Theresa of Portugal.  She was the mother of Franz Joseph II, Prince of Liechtenstein, and the paternal grandmother of Hans-Adam II, Prince of Liechtenstein.

Archduchess Elisabeth Franziska of Austria (1892–1930): Archduchess Elisabeth Franziska of Austria (1892–1930)

Maria Theresa of Austria-Este (1849–1919): Maria Theresa of Austria-Este (Maria Theresa Henriette Dorothee; 2 July 1849 – 3 February 1919) was the last Queen of Bavaria.  She was the daughter and only child of Archduke Ferdinand of Austria-Este and his wife, Archduchess Elisabeth of Austria.

Prince Karl Alfred of Liechtenstein: Prince Karl Alfred of Liechtenstein (Karl Alfred Maria Johannes Baptista Heinrich Aloys Georg Hartmann Ignatius; 16 August 1910 – 17 November 1985) was a Liechtensteiner prince and brother of Franz Joseph II.  He was the third child and second son of Prince Aloys of Liechtenstein and Archduchess Elisabeth Amalie of Austria.

Princess Stéphanie of Belgium: Princess Stéphanie of Belgium (21 May 1864 – 23 August 1945) was a Belgian princess by birth and became Crown Princess of Austria through her marriage to the heir-apparent of the Habsburg dynasty, Archduke Rudolf.  She was famously widowed in 1889 when Rudolf and his mistress, Mary Vetsera, were found dead in an apparent murder-suicide pact at the Imperial hunting lodge at Mayerling in the Vienna Woods.

Supporting paragraphs: Archduchess Elisabeth Marie of Austria Princess Stéphanie of Belgium
Answer: Mary Vetsera