When the dancer breathes, she is taking in oxygen. That oxygen energizes her muscles to move, so she can dance.
She dances fast, causing her breaths to be faster but shorter. When she breathes, her nasal cavity filters the air before it reaches her lungs. A muscle called the diaphragm, located directly under the lungs relaxes when she exhales and contracts when she inhales. It moves as quickly as her breathing.
When she finishes her dance, she takes longer, slower breaths. Her diaphragm contracts as she slowly inhales lots of oxygen, giving the lungs more time and space to expand for those longer, slower breaths.