I don't think infection rendered Maeve a complete slave who would have willingly sacrificed herself for the Outsiders, though. She wanted to usurp her mother. It might have deluded her, but she was still in the game for what she thought were selfish reasons.
Maybe she would have been willing to get blown up in the morning and spend a few decades putting herself back together as the price of knocking Mab off her throne in the long run, but I don't think she was prepared to perma-die for the cause.
She specifically says she setup someone nearby to receive the mantle, she even took Lilly out to kill Mabs obvious backup option. I think she was just out to spite her mother any way she could, and tearing the courts apart and undermining their purposes did that the only way she could.
The above quote from Cold Days shows Maeve knows some of the scope. She knows Chicago will perish. She believes the Sleepers will be freed and they will not be killed by the fail safe. And by inference she will back stab Lily. Implied by Winter and Summer going to war and the fact that Maeve is armed. It really didn't matter if Mab or Harry had gotten into the circle, Lily was toast. What Lily believes is irrelevant.
After Mab is summoned she thanks Demonreach.The obvious question is why didn't he?
Not necessarily. As long as Titania was either ignorant of Lily's part or believed she'd been talked into it by Maeve, ll Maeve had to do was make it look like her actions where a her mothers behest and Titania would probably assume Mab had gone rouge. That was her whole plan A for Dresden, make him think Mab was the one that had gone insane, no reason she couldn't be planning to try the same on Titania.
Mab and demonreach have much in common. He is there to keep the monsters locked in and she is there to keep the monsters locked out. They both understand duty and they did some bonding watching over Harry’s corpse. And Demonreach understands deals. It is much better to have Mab in your debt than to piss her off.
Doesn't track, the echoes aren't a result of the attack, their a result of the future in which the well IS breached. That means Demonreach would have to be willing to not take action even if it meant the well was breached.
The more likely answer is the old chestnut about the more power something has the more limited it's options. It likely couldn't take action without Harry's permission. And Harry didn't know enough about how the island worked or what it could do to use that. If he had he could probably have broken the circle and shut Maeve ad Lilly down in the first few seconds after he stepped ashore. I mean it's magic could see off a freaking Walker off and according to WoJ could even take Mab. Lilly and Maeve didn't really have a hope if it acted.