The first woman canonized by a Pope was …

Of course there are many women Saints prior to this canonization.

Most saints who were widely recognized by the very early Church were martyrs, as Christianity was fiercely persecuted by the Roman Empire. The faithful looked to these heroes as examples to imitate, and reminders of their own call to sacrifice.

These martyrs were called saints, though there was no official canonization process; a reputation for sanctity was based on popular acclaim, and various miracles that may have occurred through the saint’s intercession.

As the Church grew in number, there were increasing claims of sainthood and so there developed a procedure to sift through the various claims.

Initially local bishops were able to canonize individuals, but later that changed when the pope reserved to himself the right to canonize.

Pope John XV formally canonized St. Ulrich of Augsburg in 993 and then Pope Clement II canonized St. Wiborada in 1047. St. Wiborada became the first woman to be formally canonized by the pope.

Meg Hunter-Kilmer provides a succinct summary of St. Wiborada’s life in an article for Aleteia:

St. Wiborada (d. 926) was the first woman canonized by Rome for universal veneration. A Swiss hermit and prophet, Wiborada was the bookbinder for a nearby monastery. She foretold a coming invasion of Hungarian forces and urged the monks to save the most precious manuscripts by fleeing with them. But Wiborada refused to abandon her post (or her books) and was martyred. The patron saint of librarians, she’s depicted with a book in one hand and a battle-axe (the instrument of her martyrdom) in the other.

Her feast day is on May 2, and she is especially venerated in Switzerland.

This does not mean that there weren’t any female saints prior to the 11th century, just that there was no formal process at the time.