The makers of the film La Mome/La Vie en Rose used Piaf's own voice throughout until near the end when they wanted to show how she had begun to lose it. only then did they let the star of the film, Marion Cotillard, sing. Or so she said in an interview (I think she was slightly miffed since she sees herself as a bit of a singer).

So maybe not Cotillard.

I'd go along with Flossie provided Richard Bridge were not available.