Marie Antoinette is one of Maria Theresa's daughters. She was the one who decided to sent her daughter away to marry her future husband in order for Austria and France to become allies and end their ancient rivalry. Of course Marie Therese had a bad feeling about the arrange marriage and sending her young tomboyish daughter away to an unknown land, fearing that Marie Antoinette would end up in a horrible situation because of her not knowing French customs or how to be queen.
Soon problems arise as Marie Antoinette ended up in a feud with Madame du Barry, a countess and the king's mistress who was once a prostitute. While Marie Therese fears this would effect the French-Austrian alliance, she understood why her daughter was rejecting du Barry as Marie Therese hates women degrading and prostituting themselves, a belief Marie Antoinette inherited from her mother, as she herself punishes those women by whipping them and sending them to reformatories. And she also learnt of Madame du Barry's crimes in Versailles such as murdering her husband and dismissing and appointing ministers as she pleases and is controlling Versailles when it's not in her place since she is not the queen. However, she sends Count Mercy to advise Marie Antoinette to make peace with Madame du Barry regardless.
After many years in France and having three children, Marie Therese's fears of sending Marie Antoinette to France came true as she learns her daughter was ignoring her duties as queen for gambling, shopping and parties and her reputation as queen was being tarnished for her neglect and how Marie Antoinette and her family will suffer if she continues to ignore France's economic crisis. When she heads to her throne at age sixty-three, her last words were, "Love the people, Marie Antoinette, and be loved by the people." and dies in her chair, not knowing her daughter will become the most hated queen in history and she and her family will be executed.
She died on her chair at 63 age in the anime series. While in the original manga, she died her bed.