I think Maeve was infected in Summer Knight. I don't think Aurora was necessarily infected at all. We only have Lily's testimony on the matter, and Maeve—so really, just Maeve, considering how much she had manipulated Lily. Personally, I think that Nemesis had begun working on Maeve, but did it slower and more deliberately, over time; Sith wasn't done properly, which is why Nemesis had to take full control. I think Nemesis used Maeve's impotence in Summer Knight (like when she could barely control Lloyd) to manipulate her more—and Harry's flippant attitude didn't help.
Molly said that the best way to screw with someone's mind is to just enhance personality traits. I think that's what Nemesis was doing. She was always cruel, but Nemesis made her crueler.
As for the mad twinkle, I think that's specifically an indication of when Maeve lies, not a blanket sign of infection, if that makes sense.
Summer Knight is also the last book we see Lea on page before she's imprisoned, and she'd already sold Harry's debt. I take that as a sign that she had been busily spreading the infection.