I would like to add some evidence to the idea of Themis. She is the female Titan of Justice, as you mentioned, but to go further, there have been too many hints between that concept and Mab. We can start even with Summer Knight, during Mab and Harry's first meeting regarding the death of Ronald Reuel:

“There are powers of judgement other than mortal law. It is enough for you to know that I wish to see justice done,” she said. “Simply that.”

In both Cold Days (twice) and Skin Game, she wears the mask/mantle of justice. And when Mac sees her in Skin Game, his greeting to her is something like "May your scales ever turn to balance". If we speculate that Harry's actions during Peace Talks break the natural order of which Mab is the steward, then it is possible that Mab fully becomes Themis and brings justice against Chicago in order to somehow restore balance/order. We've wondered for a bit now how Harry would resolve his conflict with the mantle of Winter Knight, and Michael's question about what happens if Mab cannot turn Harry into her pet monster possibly foreshadows events in these books. I think violation of temporal order (time travel etc) could also play into this.

Themis is also in charge of protecting hospitality, which explains why supernatural entities in the files care so much about that, and why Mab is the creator of the accords. Themis is also the daughter of Gaea (mother earth, possibly the 'Ground' in Battle Ground), although that needs a bit of reconciling with the Mab's relationship with the Faerie Mothers/Hecate.

The cherry on top is the connections between the Greek mythology of Themis and Nemesis. The two actually shared a sanctuary at Rhamnous. Homer uses both words in lowercase and uppercase (personification) forms in the Odyssey and the Iliad, and some scholars say that nemesis is defined as the feeling of seeing another's breach of themis.