It is haraam for women to visit the grave of the Prophet (peace and blessings of Allaah be upon him)
Shaykh Ibn Baaz (may Allaah have mercy on him) said:
That is not permissible for them, because of the general meaning of the ahaadeeth which forbid women to visit graves and which curse them for doing so. The difference of opinion concerning women visiting the grave of the Prophet (peace and blessings of Allaah be upon him) is well known, but if they refrain from doing so that is more on the safe side and more in accordance with the Sunnah, because the Prophet (peace and blessings of Allaah be upon him) did not make any exception in the case of his grave or the grave of anyone else. Rather he forbade them in general terms, and cursed those women who do that. So we should follow the general meaning so long as there is no text that specifically exempts his grave, and there is no such text.
And Allaah is the Source of strength.