Minus the odd one or two, I've never really focused on feuds. In regards to this specific one, technically Taylor Swift has refused to name exactly who it is, but all the rumours/evidence points to Katy Perry. Essentially here's Taylor Swift said about the feud/song:
"For years, I was never sure if we were friends or not," she says. "She would come up to me at awards shows and say something and walk away, and I would think, 'Are we friends, or did she just give me the harshest insult of my life?'" Then last year, the other star crossed a line. "She did something so horrible," Swift says. "I was like, 'Oh, we're just straight-up enemies.' And it wasn't even about a guy! It had to do with business. She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me. And I'm surprisingly non-confrontational – you would not believe how much I hate conflict. So now I have to avoid her. It's awkward, and I don't like it."
I really don't get what you mean by that last line either because there are thousands of songs released today that have no relation to feuds...? (be the feud artificial or not)