I almost feel bad for her - her actual voice isn't terrible, so I'm not sure if it was nerves or just not being used to going a capella. Either way, this was painful.
The US National Anthem
actually is quite notorious for being challenging to sing without any accompaniment, because it does have a few key changes built into it that are a lot harder to nail on your own. Unfortunately, this girl definitely added several other key changes of her own.