Dancer creating music than dancing to it

At your risk.

For example expanding the principle of the theremin:

Other example.

Having a very low power FM transmitter in the room and a FM radio. Reception is interupted or modulated by dancer's movement in the room.

Or even just an FM radio barely picking up a radio station. Movement of body in the room would improve or worsen reception according to the position of dancer.

Other example:

Creating a control voltage from a light beam to photocell modulated by dancer's movement. The control voltage is connected to a VCF (voltage control filter) which filters white noise. If it works, dancer's movement should create a sound similar to sea waves braking in the sea shore.