Who is Constance the Mord-Sith from Wizard's First Rule and what is their importance?

Constance the Mord-Sith delights in doing permanent damage to her trainees and promises Richard that when he belongs to her, she will castrate him. It is the prospect of Kahlan being constantly tortured by Constance that drives Richard to agree to help Darken Rahl open the boxes or Orden.