Ah, very interesting, I hadn't considered the possibility that she was deaf.
I just rewatched the video without sound to see if I noticed anything that would give a clue to this. It's not clear at all whom she's nodding to or if it's just part of her performance; at one point it looks like she's interacting with the photographer and/or the camera.
There are a few things that make me think she is an interpreter and not a performer is that at the very end, she puts her hands up in a "Deaf wave." It seems odd that a performer would do this for her own performance, whereas an interpreter would definitely convey the applause of the arena.
Secondly, and I'm not trying to be mean here, but that was not like any true Deaf performance I've ever seen. Her signing was mostly very tight and repetitive, with very little body involvement. Deaf performers I have seen doing both this song and original poetry...well, it is ASL poetry. This just looks like straightforward interpretation, without the depth of feeling that native signers convey when performing.
Also, she was dressed all in black. Not that a performer wouldn't be, but she wouldn't have to be. She just looks like an interpreter to me, and not a native signer.
I've been on a professional sports stadium floor before the game and you can hardly hear yourself think. It's INCREDIBLY loud, so it's possible she could not hear him singing next to her nor hear the microphone feedback. That might explain her lack of communication about what was happening, in fact. Except there's no way you wouldn't hear an entire stadium singing in unison.
