In 1552 the princess, 17 at the time, married the heir to the Portuguese throne. When he died two years later, she returned to Spain.
Young, beautiful, and aware of her royal position and power, Juana was also endowed with a talent for ruling. While her brother, Philip II of Spain, was in England as husband of Mary Tudor, he made Juana regent. From 1554 to 1559 she was the effective ruler of Spain.
Juana had an additional ambition: to become a Jesuit. Telling none of her family, she informed Spanish grandee Francis Borgia, an early Jesuit, that she wanted to join the Society of Jesus.
So perilous was the project that all existing Jesuit correspondence about the situation avoids her name, using the pseudonym Mateo Sanchez, or Montoya, instead. In a quandary, Ignatius appointed a committee to advise him. It recommended that Juana enter the Society as a permanent scholastic; truly a Jesuit but forever in formation. Otherwise, with solemn vows, she would have been—according to canon and civil law—legally dead, dispossessed of everything, and incapable of ever marrying again.
With the novel, simple, and terminable vows of a Jesuit scholastic, she could have separated from the Society if necessary. When Juana pronounced her three religious vows as a Jesuit, absolute secrecy was enjoined on everyone.
She could make no obvious change in her manner of life. So, for her, poverty meant leading a rather austere life at her already simple court. Chastity meant never marrying again. Obedience—well, her letters show her sometimes trying to give orders to Ignatius and Borgia. SOURCE
The operative word here is "tried" to give orders, and the author of this article does not amplify, but elsewhere I came across Jesuits saying that Juana "gave orders" to Ignatius and Borgia. If they were followed through it would mean that the feisty woman was actually in charge of the Jesuit Order, no? They say that "Behind every great man there's a great woman", but here's an example that it actually works the other way around.