Best known for her songs 'I Kissed A Girl', 'Roar' and 'Firework', Perry bought the convent after a long battle with the former Sisters of the Immaculate Heart of Mary in Los Angeles.
Some of the remaining nuns were not happy to go ahead with the sale after watching a selection Katy Perry's music videos.
The order of nuns is now speaking out against the judgement that allowed Katy Perry to buy the convent, saying the ruling was based on a mistranslated Vatican decree.
The nuns told Fox News that her lawyers misled a judge by using the document, which they say had been translated from Latin incorrectly.
The nun's attorney, Margaret Cone, said: "Katy Perry and others will learn: you don't mess with these nuns."
Katy Perry bought the convent for around £10 million (around $14.5million) cash from The Archdiocese of Los Angeles, but the nuns wanted to sell it to restaurateur Dana Hollister instead.
The Archdiocese agreed to sell it the Perry, but the nuns said they had already struck a deal with the restaurant owner.
They said they decided who they could sell the property to, but the Archdiocese said that was not the case.
Mike Hennigan, an attorney for the Archdiocese, said: "The translation was a proper, verified translation.
"This motion appears to be an effort to delay the Court's finding that the Hollister transaction was invalid."
The judge ruled in Perry's favour earlier in the month and she is now the owner of the convent.
The Vatican has not commented on the issue.
