Is Katy writing a song about Taylor?

Ever since Taylor Swift not-so-subtly hinted that her song "Bad Blood" is about Katy Perry, fans have been waiting to hear Katy's have been waiting to hear Katy's reply. It looks like it may just come in the form of a song! "Katy thinks revenge is a dish best served cold," a source reveals. "She's writing some big, anthemic type songs that'll feature dirt on Taylor." The source even claims that Katy plans to knock Tay's to of her #1 spot. "Katy's sure that she'll be back on top, and Taylor will regret ever starting this stupid row." Ouch!