I’d not heard of her, but below is the song that was her first hit. She doesn’t have a bad voice, IMO, but I’m not sure how big her vocal range is (and the Star-Spangled Banner has a wide range), so that might have been part of the issue. The second link below has a recording of her singing tonight, and trying to reach the high notes seemed to be a big part part of her problem.
It also sounds, to me, like she was trying to add ornamentation in the high parts, which worked poorly. I’d lean towards “didn’t practice it enough,” and "tried to get fancy with it, when a straight rendition is difficult enough.
