Helle Prince Lieven
Infanta Dona Maria was never a nun. She was probably the wealthiest princess of her time, which was the main reason for her to remain single. She was extraordinarily rich. She had received a great inheritance from her father and from her mother (which after her birth Maria met just once, just before Leonor's death). She is one of Portugal's best known Infantas, because she was one of the last Avis flowers and a great protectrice of the arts and litterature...
The future King Felipe II of Spain wanted to mantain tradition by marrying her after he got widower from his 1st wife Infta Maria Manuela of Portugal, Maria's nice, but Charles V wanted him to marry the older Queen Mary I of England and Ireland, wich he did obeying his papa. After this unfortunate marriage, Charles V turned to Maria, but now she was the one not wanting to marry, especially his son...And Portugal's government did support her on this decision, because if she married a great, great, great amount of money would leave Portugal...
She remained single, dying in the reign of her great-nephew King Sebastian.