But was she actually possessed? Infected and insane but possessed? I still think that is unclear and that is why Mab wanted Molly killed if something happened to her. That is the only thing that makes sense.. Because while Molly might not run the Winter Court as Mab would, she has demonstrated that she'd do her part to protect it and the rest of the world and would with Harry's help.
What makes me wonder about Mab's insistence that Harry off Molly if Mab bites it in the fight with Ethniu is... why would Molly be worse than whoever comes next? The reasoning she gives is basically "Molly's doing a good job as Lady, but she's not ready to be Queen." Okay, so... some rando will get the Mantle and do a better job, then? And there'll be a whole new Lady to contend with, too?
I know Mab probably planned for such a contingency and made sure a good Vessel for Molly's current mantle would be on standby, but you simply CANNOT plan that well in the middle of a pitched battle. Why is Mab so confident Molly would be worse than whoever's next?
The answer is probably that Mab thinks Molly cares too much about mortals (shown in Molly's short story after Christmas Eve), but I find it really odd nonetheless.