The 31-year-old actress criticized Perry on Twitter after the singer appeared to diss Swift in her new song "Swish Swish," which appears on her forthcoming album Witness.
"'Purposeful poop' to 'bomb a petit' to a sloppy mess of writing over the top of Funkagenda..stop trying to make 'Wit..I mean 'fetch' happen," Rose tweeted to her 1.3 million followers.
"I just think with everything going on in the world to go from rebranding as political activist only to ditch it and go low.. is.. a bummer," she added, referencing Perry's support for Hillary Clinton in the 2016 presidential campaign.
Perry sent fans into a frenzy Thursday night by releasing "Swish Swish" featuring Nicki Minaj. Many speculated the song was a response to Swift's single "Bad Blood," which is believed to be about Perry.
"I've always stood up for the people I love and against things I think are cheap or mean spirited. That's not new. You have to follow your heart," Rose wrote.
"You are her fans you should buy all her songs so the songs will finally chart. If as many as tweeted me bought her last 3.. the'd be hits," she added.
"Swish Swish" includes the lyrics "Don't you come for me/No, not today/You're calculated/I've got your number/Because you're a joke/and I'm a courtside killer queen." Perry previously denied she would diss Swift on her new album.
"I think [Witness] is a very empowered record. There is no thing that's calling out any one person," the singer told Entertainment Tonight.
"One thing to note is: You can't mistake kindness for weakness and don't come for me," she qualified. "Anyone. Anyone. Anyone. Anyone. And that's not to any one person and don't quote me that it is, because it's not."
Witness will debut June 9.