Lemme clear something;
Taylor will definitely perform at the Grammys, it's like a tradition, and she's also an AOTY nominee, it's impossible to think otherwise. The question is, what will she perform ?
I think it can be Begin Again + Everything Has Changed. Everything Has Changed is quite possible, the Grammys love collaborations and Ed Sheeran is also an important nominee in Best New Artist. And the other song might be Begin Again (though i'm not so sure about that), because Taylor usually performs the nominated songs at the Grammys, i think she'll follow the tradition.