But it is the Kahlan who was willing to have a threesome with Richard and Cara. And that's canon. I am in no way saying that is a bad Kahlan!

Zedd probably has a Wizard's Rule about it. But Cara doesn't listen to him either. Who can blame her for not listening to Wizard Rules - she is not a Wizard and their magic can't harm her - and why would she listened to anyone who told her not to sleep with Kahlan