I can keep a secret for Second Sister.
But before that, Su Yunjin felt it was necessary to caution her Second Sister, lest her Second Sister be dazzled by Young Master Wu's sweet nothings.
If Young Master Wu were to cajole her Second Sister into losing her body, regret would come too late. After all, this is ancient times, and Su Yunjin knows how important a woman's chastity is in ancient times.
Although Su Yunjin is from the modern era and doesn't think it's that crucial, when in Rome, do as the Romans do, and act according to the local customs.