Her Royal Highness Seems to Be Angry, Volume 1 (novel)

Leticiel was born as a princess in a time of war and was hailed as her nation's Greatest Sorceress. After suffering a devastating loss during an invasion by a neighboring country, she gave up her life to prevent the enemy from stealing her magical powers — or so she thought. Until she wakes up and finds she's been reincarnated a thousand years in the future. Not only that, but the body she's transmigrated into belongs to a truly pitiful woman despised even by her own family. There are many things for Leticiel to be angry about, but number one on her list: why is magic in the future so lame?