Going from memory the snakes and foxes gourged themselves feeding on her channeling strength and in fact killed her in their eagerness. They learned their lesson and took their time with Moiraine.

What I took from that was that eating even a small part of a person's channeling strenght is very dangerous to the victim and is likely to kill them unless you do it very slowly. With Lanfear its not the amount that they took, but rather the speed at which they took it that was too must of a shock to her body hence she died. Then the DO recycled her and she was stuck with the loss where as if she had been reborn naturally she would have probably reverted to her default soul strenght.


AMoL Spoilers



Saying that some of that may be contradicted by a few references I recall in my very rushed first reading of AMoL but then again it might be put down to the character who we have the pov from being simply wrong or mistaken.