A true 44.1kHz FLAC will show frequencies up to 22.05kHz. Any sudden brickwall at 16kHz or 18kHz indicates a lossy source.
Her voice moves from a near-whisper (“Let the sky fall”) to a chest-belting roar (“When it crumbles”). MP3 compression can introduce audible artifacts in the loud parts and hiss in the quiet parts. FLAC handles these swings with zero distortion.