Is it permissible to return the wife to her husband's عصمة (bond of marriage) during the last days of her menstruation, after the bleeding has stopped but before ghusl (ritual bath), and is that period counted as part of the waiting period ('iddah)?

If one doubts whether menstruation persists or has ended, the default is that menstruation persists. And if one doubts whether the revocable divorce (raj'ah) occurred before or after the 'iddah (definition) period expired, the default is that it occurred within the 'iddah, making it valid. This is based on the jurisprudential rule: "Certainty is not removed by doubt."