What is the ruling on performing one ghusl with a single intention for purification from menstruation and for entering Islam for a woman who embraced Islam during her menses or shortly after its cessation?

A person afflicted with obsessive thoughts should not pay attention to them. Turning away from obsessions is the most beneficial treatment after seeking refuge in Allah from them. This is supported by the hadith of Abu Hurairah (may Allah be pleased with him), who said that the Messenger of Allah (peace be upon him) said: "Satan comes to one of you and says, 'Who created such and such? Who created such and such?' until he says, 'Who created your Lord?' When he reaches this point, let him seek refuge in Allah and stop."

As for apostasy from Islam, it only occurs with certainty. The default state is the persistence of Islam, and apostasy does not occur unless a Muslim commits a statement, action, or belief that is definitively proven to be major disbelief by the Qur’an, Sunnah, or scholarly consensus. No specific individual is judged to be an apostate unless the conditions for declaring someone a disbeliever are met and the impediments to it are absent, such as reaching puberty, sanity, free choice, and not having an excuse due to ignorance or misinterpretation. Therefore, one whose apostasy has not been established is not required to perform ghusl (ritual bath), because apostasy must first be proven. The ghusl for a disbeliever upon embracing Islam or for an apostate is recommended, not obligatory. Thus, you are only required to perform ghusl from menstruation.