this YouTube video clip of "All Alone am I".
The Wikipedia entry on Brenda claims that her "popularity faded in the late 1960s as her voice matured". I would put it differently, maybe her voice 'changed', but I thought Brenda's voice was mature when she was a teenager.
Brenda Lee is still performing. She's scheduled to be in Wichita August 14th. I don't think I'll go. I don't want to risk damaging the naughty image of her I conjured up as a boy listening to Sweet Nothings.