Here's what Kim has to say about it:
"The first Hollows graphic novel is due out July 12, 2011, and I finally have a cover to show you! If you’ve not heard, this takes place in the golden year where Ivy and Rachel work together at the I.S. Rachel is the intern, but you can imagine she’s not taking a back seat to her vampire partner. This was done from Ivy’s point of view, and since Kisten was still alive during this time, we get to see him. In a tub, no less. -grin- On a more personal note, I want those boots."
I'm super excited for this, not just because it's Kim Harrison, but because it's a graphic novel. I love when authors mix it up, and we get to see their characters in action and color. I'm stoked for July. It's going to be amazing.
Source: Kim Harrison's Blog