In Cold Days on the way to the Outer Gates, Mother Summer and Harry talk as they go. On page 327 she says a couple of things that caught my eye upon rereading.
I walked for a little while, considering that. "You are saying that I have a chance to stay me."
"I'm saying many things," Mother Summer said. "Do you have a chance to remain yourself despite the tendency of the mantle
to mold your thoughts and desires? All Knights, Winter and Summer, have that chance. Most fail."
"But it is possible," I said.
She looked up at me and her eyes were deeper than time. Anything is possible."
"Ah," I said, understanding. "We're not really talking about me."
"We are," she said serenely, turning her eyes away. "And we are not."
"Uh," I said. "I'm getting a little confused here. What are we talking about, exactly?"
Mother Summer smiled at me. And then she clammed up. We are? We're Not?
I think this means that Mother Summer knows what Mab's plans are for Molly whether Molly becomes Summer Lady or as turned out, Winter Lady. However because that is in the future and would affect how Harry was about to act, and the stakes are too high to mess any of that up. Mother Summer won't tell Harry there is any plan for Molly, her name isn't even mentioned. However Mother Summer does tell Harry he has a chance to defy the odds and remain himself even with the Winter Mantle. Then she gets cryptic and hints that it isn't just him that has a chance to keep his own identity. The only one I can think of is Molly, who as we know by the end of the book is about to become one of the Ladies. If Harry ever remembers this conversation he should be reassured for Molly.
Now this could be part of some deal that Mab made with Uriel ahead of time, so that she could make Molly one of the Ladies. Because of Michael and his service I doubt that Uriel would go along with Molly losing her soul to become one of the Ladies,no matter how important for the cause that Molly become one of the Ladies. So I imagine Mab agreed to allow that choice, and Molly has a chance to remain very human with a soul even as a Fae Lady. Actually there is some evidence that this was explained to Michael and perhaps Charity as well, since they both took the fact that their daughter is now a Fae Lady very well, which I don't think they would if they thought Molly was losing her Immortal Soul.
It may also be why in Battle Ground Mab ordered Harry to kill Molly if she were killed and Molly become Queen. Mab fears that an all too human Queen wouldn't be up to the job. Also maybe why she is pushing Harry to marry Lara..