LOS ANGELES — Stepping up her fight to buy an eight-acre convent and retreat house here, the singer Katy Perry last week sued a rival would-be purchaser, whom she accused of interfering with her contractual and other rights.

In documents filed Thursday with the Los Angeles County Superior Court, Ms. Perry said Dana Hollister, a developer who is also trying to buy the convent, “took advantage of vulnerable, elderly nuns, who she malevolently convinced to oppose the Roman Catholic Church” by rejecting Ms. Perry’s $14.5 million offer for the convent.

For months, the abandoned convent and its retreat house have been the object of litigation among Ms. Perry, Ms. Hollister, the Roman Catholic Archdiocese of Los Angeles and a pair of aging nuns who have disputed diocesan attempts to control what was once the headquarters of their now-diminished order. A judge ruled this month that Ms. Hollister could pay monthly rent to the nuns, even while vacating the property pending final decisions about its sale.

Ms. Perry’s lawsuit names both the archdiocese and the nuns’ order as defendants in a plea for clarification of her rights. The complaint made no claims against the nuns, whom it described as “victims” of Ms. Hollister.

Representatives of Ms. Hollister declined to comment Sunday on the complaint.