Francis, who has sought to reform the Catholic Church's governance, named the nun as Prefect of the Dicastery for Institutes of Consecrated Life and Societies of Apostolic Life in a historic "first", a Vatican official told AFP on Tuesday.
The 59-year-old Brambilla is a former nurse with missionary experience in Mozambique who was previously deputy of the dicastery, the Vatican term for government ministry or department.
Brambilla is "considered moderate and conciliatory", with "respectable experience as a missionary in Africa and as an administrator", Vatican journalist Franca Giansoldati wrote in the Messaggero daily.
But she and other Vatican experts questioned Francis's decision to appoint a cardinal as "pro-prefect" alongside Brambilla.
The Vatican did not explain what would be the role of Spaniard Angel Fernandez, 65.
The term pro-prefect has traditionally been assigned to a person set to eventually take over the role of prefect, according to the Cruxnow.com religious website.
Giansoldati said those fighting for women to play a greater role in the Church were "perplexed" by the double appointment, and concerned Fernandez would have the real power, with Brambilla reduced to a figurehead.
Cruxnow wrote that "because heads of some Vatican departments make binding decisions in the name of the pope, sharing in the exercise of his power, they therefore need to be in Holy Orders, meaning ordained to the priesthood".
'Unique'
Sisters or nuns far outnumber priests -- with 559,228 sister or nuns in the Catholic Church today, compared to some 128,559 priests who belong to religious orders, according to Vatican 2024 statistics.
But women cannot receive Holy Orders, and repeated calls by some for women to be permitted to become priests have come to nothing.
Born in Monza in northern Italy, Brambilla trained as a nurse before entering religious life.
In an interview with Italy's Corriere della Sera newspaper she described being influenced by the "different, unique, sacred stories" told to her by those she met during missionary work in the late 1990s.
She later gained a doctorate in psychology before becoming head of the institute of Consolata Missionary Sisters from 2011 until May 2023.
Francis has been naming women to more elevated positions within the Holy See since becoming head of the world's almost 1.4 billion Catholics in 2013, but progress is slow.
The percentage of women working in the Holy See and Vatican City has risen from around 19 percent in 2013 to 23.4 percent in 2023, according to data published by Vatican News.
In October, a Vatican assembly on the future of the Catholic Church said that more should be done to help women overcome "obstacles" to taking leadership roles within the Church.
It said calls for women to be allowed to be ordained as deacons should continue to be debated.
Unlike other Christian denominations, the Catholic Church only allows men to become deacons, who can officiate baptisms, weddings and funerals but not mass.
