After 11 episodes it should be pretty obvious, at least it is to me, that Yuuki would never sacrifice somebody to save someone else. She would sacrifice herself, though, like she has been doing by giving her blood to Zero, often even offering it without being asked when she has happened to meet Zero. It would be quite a breach of personality in my opinion if she suddenly went and shot a dear friend simply because someone hostile told it would save another friend (what a wonderfully reliable source of information, as well).