She was Archduchess of Austria only titularly. All of her siblings were Archukes/Archduchess of Austria, as it was common to give this title to the children of Holy Roman Emperor. In fact, Austria was then ruled by Marie Antoinette's mother, Maria Theresa.
Yes she had a younger sister, Archduchess Maria Anna of Austria (1718-1744) who was Governor of the Austrian Netherlands and died in childbirth at the age of 26.
Maria Theresa and Phillis Wheatley are important for different reasons. Maria Theresa, who was Marie Antoinette's mother, was archduchess of Austria. Phillis Wheatley was a very intelligent slave who was a poet. Her first poem was published at the age of 12.
Archduchess Maria Anna of Austria was born on October 6, 1738.
Archduchess Maria Anna of Austria was born on October 6, 1738.
Archduchess Maria Clementina of Austria was born on 1777-04-24.
Archduchess Maria Clementina of Austria died on 1801-11-15.
Archduchess Maria Dorothea of Austria died on 1932-04-06.
Archduchess Maria Dorothea of Austria was born on 1867-06-14.
Archduchess Maria Isabella of Austria was born on 1834-05-21.
Archduchess Maria Isabella of Austria died on 1901-07-14.
Archduchess Maria Immakulata of Austria died on 1968-11-25.