Sister Catherine Rosse Holzman, 89, died in court during the proceeding related to the sale of a Los Feliz property, according to ABC-affiliate KABC.
A judge ruled in 2016 that the nuns' sale to Hollister was invalid, paving the way to a purchase by Perry from the Archdiocese of Los Angeles.
Despite the nuns' attorney, Margaret Cone, claiming the L.A. Diocese knew the final decision was pending at the Vatican's Dicastery, Judge Stephanie Bowick let a jury award the L.A. Archdiocese and Perry $15 million in malice and fraud damages against Hollister.More news: Cristiano Ronaldo Brace Sees Real Madrid Past Eibar in La Liga
During an interview in 2015, she explained: "After she spoke [about] her lifestyle, and what we have been teaching for years and our older sisters have been teaching, and what we believe in, [she] just did not fit".
"Katy Perry, please stop", Holzman told Fox 7.
At the time of Holzman's death on Friday, she was in court for a post-judgment hearing on the case, TMZ reports.
The sisters said they previously spoke with Archbishop Jose Gomez, who agreed they could choose who would purchase the property, but they could not get a hold of him once they chose to move forward with Hollister, The Los Angeles Times previously reported.More news: Arsenal thump Watford 3-0 in Premier League
The singer agreed to buy the eight-acre property and its Roman villa-style buildings for $14.5m (£10.4m) in 2015, but the deal failed when its former residents objected.
"Rest with the angels our most precious treasure". "We extend our prayers today to the Immaculate Heart of Mary community and to all her friends and loved ones", he continued.
At issue in the ensuing legal battle was who had the right to sell the property - the Archdiocese or the nuns.
Another of the nun's concerns is with the singer herself.More news: Kane injury overshadows Tottenham win
Perry reportedly visited the nuns to win them over, and is said to have shown them her tattoo of Jesus and sung a hymn for them.
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