Ok so let's think of the favors Lara could've done. One thing that comes to my mind is helping to defend Demon Reach. If that's the favor, then Winter owes Marcone a favor too since his forces helped defend it too.
I think one of the favors might have been Thomas assassinate some one.
In chapter 6 Harry talks about the amount of influence Lara is gaining in the government. In Jury Duty, we meet Tania Raith, a low level DA, who could exert influence over DA's higher up in the food chain. Mab may want to use the mortal authorities and Murphy as leverage over Harry. Perhaps Lara helped Mab get that influence.
Another thing that i found interesting was this:
"“New colors,” she said, her voice velvety smooth and calm. “The shield used to be blue. What changed?”
“He made an alliance with a powerful guardian entity,” said the second monster, a woman seated beside the first. She was as lean as a rod of rebar, but colder and harder, and her opalescent green eyes were too big to be strictly human. Silver‑white hair fell to her shoulders, today in a fine silken sheet. Her voice sounded calm and precise, and she wore a glacier blue dress that belonged on a runway. “It does not interfere with his duties.”"
That exchange between Lara and Mab makes me wonder how Harry's relationship with demon reach has changed him, and to what degree Harry can use power from Demon Reach when he isn't on the island.
Mab also implied that Lara would like how Harry tasted and remind her that Harry was a member of her court. When Harry and Mab had sex to seal the deal for winter knight she said that Harry was hers. I also think Bob may have mention something about Harry kind of being married to Mab. I wonder if Mab protects Harry from being eaten by a wampire.
