Sister Pasqualina Lehnert was a Bavarian Roman Catholic nun who served as Pope Pius XII's housekeeper from his period as Nuncio to Bavaria in 1917 until his death as pope in 1958.

Sr. Pasqualina's position as Pius's longterm housekeeper caused friction in his relationship with members of his family and with senior figures within the Church. His sister Elisabetta Pacelli, who had a long-running fued with Sr. Pasqualina, called her "scaltrissima"-- extremely cunning, while the Pope's nephew frequently begged his uncle to dismiss the Bavarian nun.

In 1918 rumours of a sexual relationship between the then Archbishop Pacelli and Sr. Pasqualina reached the Vatican. Pacelli demanded and received a full Vatican investigation at the highest level of what he called this "horrible calumny". The investigation exonerated the Archbishop and Sr. Pasqualina of any wrongdoing.

In the pope's final years, as his health deteriorated, critics maintained that Sr. Pasqualina in effect controlled the pope, by deciding who could see him, when they could see him, what documents he could read and advised him on decisions he should take. Enemies of Sr. Pasqualina labelled her La Popessa.

Her intense dislike of him was credited by Curia members with causing Pope Pius XII to deny a cardinalate to Archbishop Giovanni Montini, the future Pope Paul VI, so excluding him from the 1958 papal conclave, where it was suspected that he would have been a leading candidate to be elected pope. This decision was overturned by the new pope, Blessed John XXIII, who chose Montini to be the first person he appointed to be a cardinal.