I read this novel in approximately 2005, in America. It was marketed for adults.
It was set in a fairly typical medieval-esque fantasy setting. The main character was a woman, and I think she could use magic. The main conflict of the novels was between the woman and a character who I believe was her brother. Her brother is a ruler, and he fights the main character with military force.
At some point during the novel, the brother's friend is killed and he refuses to accept his friend's death and treats him as if he were alive. There is a particularly evocative scene where the dead friend is propped up at a feast table while his decomposition is described in detail, but the brother still acts as if he is alive. All of the brother's subordinates are too terrorized by him to admit that his friend is dead.
I also remember that the end of the book gave a quick summary of all the characters' lives after the end of the plot, and that the main character lived for many years but then died of (uterine?) cancer.
I believe this was a single book, but it also may have been a duology. It definitely wasn't part of a trilogy or a larger series.