Good thing they actually heeded the warning bell. But then again, the duchess is not ordinary noble, whose main interest would be to maintain her own prestige and face. After all, she had none in the beginning (as far as she knows, having been kidnapped so young). So, she can be decisive when she feels like it's the right moment. If she was an ordinary noble, she might be more prone to thinking that she could become a laughing stock by believing in an old legend. On the other hand, she's loved by the duke, so as long as she can honestly say she did what she did with the best interests of the dukedom in her mind, the duke wouldn't get angry. Technically the bell still remains an alarm system, even if next to nobody believes in it, so again technically her decision even isn't hasty.