The whisper in red

I had been watching TV
And as often happen when I watch
A minute sleep only
A wisp of a young woman in a red ballerina dress.
Sat on the floor leaning her head at my leg.
When seeing I was awake, she got up
And disappeared silently as a falling leaf.
Later that evening I watch a French art program
And the lady in red was painted 120 years ago.
Was the one, the expert, spoke about
They knew it was Degas but none knew who she was.