As I understand from the comments, this is about an incident in which Taylor Swift performed a song she wrote for Rihanna at one of her own concerts?

Covers are a very normal thing, especially in a live setting, and it's not usually expected to provide context for those covers during the set, just don't put them on the live album as your own work. I guess when you're as big as Taylor Swift it could be a different issue, but if I were a Rihanna fan I'd probably see it as a gesture of respect, or intended to provoke recognition among fans of other pop music (or of Taylor Swift's songwriting) unless there was some indication otherwise. I'd still call it a cover if she wrote it for Rihanna, but that's largely immaterial.

I'm inclined to think this is just regular celebrity drama BS... whoever you side with is usually about who you personally like, but the whole thing is ultimately petty.