With the exception of discussions about S4, you need to be unavailable to her.
She is looking for validation that she made the right decision by leaving, and you played right into it by taking her call. We talked about getting "tagged" if she came over the other night; this is the same thing.
"Let me check and make sure John is still waiting around for me. Yep, sure is. He took my call, then told me to put gas in my car. He even stayed on the phone until I was done with him. He's okay, and clearly still stuck on me, so I can leave him for a while and come back when I'm ready. I'm sure he'll still be here..."
Let her wonder about you, and let her feel the consequences of leaving.