Greetings all! Back in middle school, so in my case post 2015 but pre 2020, I read a book from off the shelf of my language arts teacher. I remember it was paper back and had a primarily red cover, with I think a depiction of a city built on top of a desert, mesa plateau type area? I remember the book followed I think 2 different perspectives, though I don't remember if it was switching 1st person or 3rd. One character was the princess of the aforementioned city/nation, and the other was I believe her appointed royal guardian type? The book was very much a YA fantasy, of course, and I assume there would be romance subplot later in the book/series. I don't think I finished it before the year ended, though, as I'd started reading it in June. Anyway, very near the start of the book, this kingdom goes to war with one (or maybe multiple) of the surrounding factions, which starts the main plot beats.
If memory serves, the princess and the royal guardian guy split up at that point, she travels away from the kingdom in order to stay safe, as I believe the king was pretty sure they were gonna lose the war. There's a scene I remember when I think she's at a halfway point, possibly still with her knight, in a commoner house, and she has then draw a bath for her, and I think she teases either the knight or one of the young men who live in that house? And then sometime after that she leaves and eventually ends up with a sort of tribal people in the canyons of the desert, where I believe she starts learning some ancient form of magic. That's all I remember from her side of the story, though.
As for the knight/the rest of the kingdom, the only other plot beat I remember is the king complaining about how when the nobles show up at their encampment for that war, they've brought all their luxury items and servants with them. I feel like I remember specifically one noble bringing a golden tub with him. And the king is lamenting about how they've all grown soft and fat on their laurels, and how they're definitely gonna lose now. And I believe very quickly they do, in fact, get their butts whooped by the aggressing factions that have come to conquer. For some reason in my mind this series is called the Fallen Kingdom series, but when looking that up I get completely different books. I also believe the princess's name started with an S, but that's all I remember.
Any and all help is appreciated, thank you much!