So, I just picked up this little detail on my umpteenth re-read.  At the party, just after Lea had absorbed Susan's memories, Thomas shows up with a blackened lip shaped mark on his neck -

I glanced over at him.  There was a mark on his neck, black and angry red, like a brand, in the shape of lovely feminine lips.  I would have thought it lipstick, but I sensed a faint odor of burnt meat in the air. 
"What happened to your neck?"
His face paled a few shades. "Your godmother gave me a kiss."

So I'm thinking since she had all of Susan's memories of Harry, it was like she was feeling her love and therefore anathema to a White Court Vampire?

Sorry if this has been discussed before, but I just ran across it and felt the need to bring it up to someone...