Although Marie Antoinette is the most well-known daughter of Maria Theresia, during her mother's lifetime it was another daughter, who provoked the most scandal and was her mother's greatest problem child.
Maria Amalia (1746-1804) was kind of isolated in the family as although being part of many siblings her elder and younger sisters were some years apart of her and so she was educated alone. At 22 she fell in with Karl of Zweibrücken and hoped to marry him.
Her elder sister, Maria Christina, had after all also been permitted to marry for love. MA was furious, when she was forbidden to wed him and instead had to marry Duke Ferdinand of Parma. This created a first lifelong discord between mother and daughter.
Ferdinand was a weak character and soon enough MA dominated him.
Her mother constantly warned her not to interfere in politics, but MA wouldn't listen. It came up to the point were MT stopped corresponding with her daughter alltogether and also forbade MAs siblings to do so (though at least Maria Carolina and Maria Anna still did). MT later on tried to reconcile with her daughter prior to her death, but to no avail so they didn't have any contact before her death in 1780. MA died in Prague being forced out of Parma from Napoleon's troopes.