She has a Looper pedal on the stand beside her, she switches it on and off here and there. The same as Ed Sheeran does when he plays live on stage.
Using one of those and keeping everything in time is a fine art in itself.
It records what you play and keeps repeating it as you move on to the next part. You can slowly build up a whole orchestra by laying down section on top of section.
She is playing it all though and its very clever stuff.
