An 89-year-old Catholic nun who has battled pop star Katy Perry for years over the sale of a Los Angeles convent has collapsed and died while attending court proceedings about the case, according to media reports and supporters.

Sister Catherine Rose Holzman, one of two ageing nuns who were fighting the sale of the eight-acre (three-hectare) convent, died on Friday in Los Angeles county court, Fox affiliate KTTV reported.

The Sisters of the Immaculate Heart of Mary property in the Los Feliz area of Los Angeles that pop star Katy Perry is buying Photograph: Nick Ut/AP

Holzman had earlier told KTTV as she entered the courthouse with Sister Rita Callanan: “To Katy Perry, please stop. It’s not doing anyone any good except hurting a lot of people.”

On Saturday a website set up to back the nuns’ legal battle carried a picture of Holzman with the caption” “Rest with the angels our most precious treasure.”

A spokeswoman for Perry, one of the world’s top-selling pop stars, did not immediately respond to a request for comment. The Los Angeles county medical examiner and the Archdiocese of Los Angeles did not respond to queries about the cause of death.

At the center of the legal dispute is the property Holzman and other members of the Sisters of the Immaculate Heart of Mary had once lived in.

Holzman and Cullanan, among five nuns who had lived at the convent, had sought to sell the property for $15.5m to restaurateur Dana Hollister, who wanted to convert the property into a hotel.

The archdiocese sued to block the sale in 2015, arguing the nuns did not have authority to sell the property to Hollister.

A judge ruled in 2016 that the sale was invalid, paving the way for Perry to buy the site from the archdiocese.