I really appreciate the distinct characterization of Kel as she's introduced in this book. The vast majority of Strong Female Characters I read fit one of two tropes - quick tempered, loud, and brash (Alanna the Lioness, Aelin, etc), or quiet, devious, and often very sexual (the prostitute/courtesan spy is the classic trope coming to mind here). With Kel you get a heroine who is still very straightforward and says what she thinks, but has enough restraint to only pick the battles worth fighting. She has a rein on her temper but won't abide a bully, and I love it.
This series is also missing a Major Love Story, which I personally love. I think this is an ideal series for any young adult (or older!) to read.