Originally Posted by powersackers
Lydia wants Skylar dead. She knows Skylar was involved. Lydia us One of the few who could testify against Sklar.
No disagreements she wants Skyler dead, but as of now, there's nothing she could say in court about Skyler that implicates her. What does Lydia know about her? That she runs a car wash? Presumably Walt sure never told Lydia anything about Skyler's participation.
Now, if Lydia decides to kill Skyler out of fear for her own freedom, that would certainly give Walt a reason to kill her. But like I said, if Walt wants to kill Lydia, he won't waste his time trying to pull off poisoning her.