It is presumed following some deductions and testimonies that she was born on the 26th of July 1604. As her christening certificate was lost in the fire of the Main Church of Arequipa in 1620, before the first cathedral was built, we cannot know the exact date.

Ana was the fourth of eight children, born from Sebastián de Monteagudo and Francisca de León. They were: Francisco, Mariana, Catalina, (Ana), Juana, Inés, Andrea and Sebastián. It is known that Francisco became a priest, Mariana married Gabriel López de Pastrana, Catalina married Gonzalo Tamayo and Inés married Bernardino de Meneses. Of the others, nothing is known, but it is possible they died from one of the plagues, which struck Arequipa in those days.

Sor Ana was delivered to the Catalina nuns when she was three years old, to be educated and instructed; in those days mainly moral and religious teaching.

It is believed that her parents took her from the Monastery when she was ten or eleven with the intention to marry her when she reached at least fourteen, because in those days the parents made betrothals of their children, even below the fourteen years of age the minimum age for a valid marriage.

While she was at home, she had a vision of Santa Catalina of Siena, showing her the habit of the Domenican nuns. Then she decided to return to the Monastery, being led by a small boy called Domingo.

When her parents learned the fact, they tried to dissuade her by offering her jewels, but she kept firm in her decision. At least her father accepted her decision and supported her but her mother could not accept it, telling her never to come back home.

The dowry she was to pay on entering the Monastery was paid by her brother Francisco. Her Mother, even though she was able to cover it, definitely refused to pay it.

Ana took her vows, taking the name of "de los Angeles". From the beginning she practiced what she had vowed, always seeking perfection.

Once, she was elected Mother Prioress of the Monastery for a three-year period, a most important post that she tried to decline, thinking she was not capacitated for the position.

Some of the nuns backed her and promised to help her, but others were against her, saying how someone who could not read or write would become a Prioress. That position caused her many problems with other nuns, who even in three opportunities tried to poison her.

They were against the rules of austerity imposed by Sor Ana during her charge, obliging the nuns to wear the habits without gold ornaments.