VV only killed Marianne because she agreed with Charles. Most probably she was also the only 'queen' who knew about Charles plans.

Rewatching the preview I believe that Kallen is walking besides Lelouch, meaning (hopefully) she has sided with him once again... or at least she is there trying to confirm her own purpose as she said on this episode...

30 Second Preview
http://www.youtube.com/watch?v=wl36bui7-EQ