YA Fantasy/ Adventure of girl who infiltrates fancy school as a servant to solve her parents' murder. Read around 2014-2018. Spoilers ahead.

[Drew]

I read this book somewhere between 2014-2018, likely, so my memory is very vague. It wasn't an old book; it read like modern-ish YA, I think (definitely not written before the 90s at the earliest, I'd say). It's possible that instead of being a servant, she was a slave, but she infiltrated the place herself, and I'm fairly certain it was to solve her parents' murder. A couple key plot points/details stick out in my mind (again, spoilers ahead):

1. The headmaster of the school (a woman) was revealed to be the killer of the girl's parents, or somehow connected to their murder.
2. The headmaster, as punishment for... something? carved a "K" into the girl's skin-- I think on her back (I think it was the headmaster's initial? Regardless, I'm almost positive it was specifically a "K", but if you know another book that has someone carving a letter in general, it's possible I misremembered).
3. At some point, the girl leaves the school in secret to visit a local village and there's some kind of festival going on while there. I think she wore a mask (masquerade party? But the image I had in mind when reading it was outside). There may have been a love interest she encountered there, but I'm not sure.
4. Not exactly a plot point, but this book was definitely in a made-up world, I think (not taking place on Earth, I don't believe). There wasn't any modern technology, but it wasn't a historical fiction book, which makes me more certain it was in a fantasy world. Magic may have been involved in the book but it doesn't stick out in my mind.
5. I read it in English, and I imagine it was published in English. I don't remember anyone else I knew having read it, I just randomly found it at the library.

If anyone knows this or it sounds at all familiar, I'd be so grateful. This book has been stuck in my head since middle school and I have no idea how to find it.

[Rainbowheart]

Does anything on this list look familiar?

I Go To A "Special" School

[anonymous]

old post but I am almost %100 certain this is An Ember in the Ashes by Sabaa Tahir

[Bargle]

Link for Anonymous's suggestion. An Ember in the Ashes by Sabaa Tahir