That does happen, but only after additional crimes, including gathering forces with mind control by manipulating one of the heroes and using those forces to stage a coup, coming close to killing her parents and usurping the throne. The exact punishment leaves a bad taste in my mouth, they could have just executed her, but monarchs don't take kindly to that sort of thing. A death sentence makes sense in any sort of medieval royal context, the cruelty is due to the combined malice of everyone she's wronged over the course of her life