You have to get the mouth right...

... as if you're kissing a baby.
That's how you get the wonderful sound Sue makes with her shiny new flute. (Decades of practice helps, too.)

She had the correct specs on in this shot, but for her subsequent appearance she didn't, and she was playing Handel's Arrival of the Queen of Sheba - a demanding piece even when you can see the music. She nailed it though.
Fabulous.