Is not a wife's telling her husband about a sin she committed considered an open declaration of it?

There is no contradiction between a woman informing her husband that the condition upon which her divorce was suspended has occurred, even if it was a grave sin, and the prohibition against openly declaring sins. This is because informing the husband in this context is not among the prohibited open declarations, due to necessity, just as an admission before a judge to establish a hadd (prescribed punishment) is permissible. The prohibited open declaration is the tearing of Allah's veil and speaking about sins without a legitimate Sharia purpose. The woman should not mention the details of what befell her; rather, she should suffice by stating that the condition upon which her divorce was suspended has occurred. The husband must conceal her and be evasive if asked about the reason for the separation.