Old Matriarch, Young Again

After foreseeing her noble house wiped out, an aged matriarch drinks a secret elixir, becomes young, and seizes control. With unmatched skill in combat, letters, trade, and traps, she tames rebellious heirs, exposes a plot-stealing time traveler, crushes her schemes, foils a prince's coup, cures poison, purges traitors, and saves the realm.