Not sure I've read anything that would make me see it as "young adult". It's an interesting series, like Crown of Stars (CoS) embedded in a more-or-less historical content. Like CoS it is an alternate history, where Carthage survived, and where African people moved to northern Europe because of a plague of zombie-like beings. These things are not foci, but background that allows Europe to be multi-racial in a way that was extinguished in our world during the dark ages. The timeframe of the Spiritwalker world is early modern, rather than medieval. It is, in consequence, an interesting world.
At this time, the two published books are Cold Magic and Cold Fire and the upcoming conclusion of the trilogy will be Cold Steel. This relates to one system of magic in the book, though the protagonist belongs to another magical system, that of the Spiritwalkers.
I really liked these books, found them interesting and engaging, less rambling than CoS, but not quite as engaging as Elliott's Crossroads series, which is my favourite of Elliott's series. Like CoS, Spiritwalker is an earth-based series that draws heavily from studies of technology and history to create a really believable alternate world. I think that is one of Elliott's strengths, and IMO, the reality of her environments really puts her writing into a class above most fantasy
