The Cunning Princess Consort

Protagonist marries the Prince, foils schemes with anti-fraud skills. Seraphina Winslow, his first love, plots against her, but she foils her. Secretly sterilizes the Prince. Topples Empress Dowager's power. Prince dies from poison. Protagonist supports adopted son to throne, becoming Dowager Princess. Dismisses concubines, settles Seraphina Winslow, takes control, lives a stable, free life.