YA Fantasy Book circa 2003 taking place in a keep/castle under siege

Hi folks! I read this book in 7th grade as part of a project to pick a book off of a "banned book" list. Presumably it was on the list due to being including magic and iirc, undead? I don't remember much, but it was a fantasy novel hardcover where most of the story took place inside and just around a castle or keep under siege.

I believe there was a main young male and young female character, have vague memories of a scene in a great hall/dining hall, one of the main characters being sorcerous/witchy, maybe died? Almost died? Was thought to be dead?

For some reason, my memory is that the cover had a white tiger on it.

Good luck and godspeed, and I hope I'm remembering these few vague details well enough to find it! Thanks!