A woman of power. A witch. Jadis implies the power to bind and a caring, but relentless sadism.
Jadis is the white witch from the Chronicles of Narnia. Possibly modelled on a a noted Oxford dominatrix of the time that Lewis was writing the Chronicles.
A woman of almost magical power who causes great, but irresistable, suffering
My mistress is such a jadis that I can no longer close my legs without moaning