I'm pretty sure that was a personal warning to Harry. He's always denied Molly the one thing she wanted. Him. As Queen she could have him. And Harry wouldn't have a choice. Molly's a little twisted, at least the way Jim has written her. That might make her a lot twisted. The quote is.
“As Winter Lady, she shows promise,” Mab said. “But she is not ready to become Mab. The consequences would be . . . unsettling. For both of you. Perhaps for all of Winter.”
Butcher, Jim. Battle Ground (Dresden Files) (p. 220). Penguin Publishing Group. Kindle Edition.
As long as her emotions rule her still Harry would be in danger.
Probably not. But there's two things to consider regarding the possible hosts.
- Justine knew Molly was there in the circle. If she was infected, then Nemesis likely knew. If Maeve was infected, then Nemesis could have told her in her head. So she might have meant Murphy, or she might have meant Molly.
- There were nine Sidhe in each retinue, not counting Red and Rawhead. That's at least nine candidates of Summer Sidhe that should have been compatible if they were female, and possibly some from Winter in a pinch. The question is, were they all male by design, or were there any females? If so, were they potential hosts as well?
I don't think that the infection works like that. I think it's an amplification of something that is in everybody, some weakness. And the infection acts like a reinforcement of that weakness. That's basically how it worked with Cat Sith. He hated serving Harry and the voice whispered to him to kill Harry. When Harry points it out, Cat Sith resisted and was destroyed. I'm not sure that there is anything left of Justine.
Mab on the other hand had Molly prepared, however the Queen does that kind of thing. It was Mab's choice where that mantle went.