Allah says in the Qur'an, "And they will ask thee about [woman's] monthly courses. Say: "It is a vulnerable condition. Keep, therefore, aloof from women during their monthly courses, and do not draw near unto them until they are cleansed; and when they are cleansed, go in unto them as Allah has bidden you to do." Verily, God loves those who turn unto Him in repentance and He loves those who keep themselves pure." (Qur'an: 2: 222)
According to this verse, as further explained by the traditions and practice of the Prophet (peace be upon him) a woman ought to cleanse herself following the expiry of her menses before her husband can have conjugal relations with her. It is not allowed to combine the two ghusl.
If, however, someone failed to observe the rule due to ignorance, they ought to ask forgiveness of Allah and resolve never to do it again. Allah is indeed Forgiving, and Merciful.