All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Among the conditions for the validity of the I'tikaaf (i.e. confining oneself in a mosque with the intention of worship) is that it has to be observed in the mosque, and according to the opinion of the majority of the scholars it is not valid for a woman to observe I'tikaaf in her prayer room at home. Allaah Says (what means): {…while you are in I'tikaaf in the mosques.}[Quran 2:187]. Her prayer room at her home is not called a mosque.
Al-Mardaawi from the Hanbali School of jurisprudence, said: ‘‘…She (a woman) may observe I'tikaaf in any mosque apart from her prayer room at her home; this is the preponderant view of our School of jurisprudence, and the view of the majority of the scholars of our School, because the woman's prayer room at her home is not a mosque neither in reality nor by decree.’’
Moreover, An-Nawawi said: ‘‘It is not valid for a man or a woman to observe I'tikaaf except in the mosque, and it is not valid for a woman to observe I'tikaaf in her prayer room at home, and it is not valid for a man to observe I'tikaaf in his prayer room at home, this is the preponderant opinion of our School.’’
The evidence that it is not valid for a woman to observe I'tikaaf in her prayer room at home is that the wives of the Prophet did not observe I'tikaaf in their prayer rooms at home; had this been acceptable, they would have done so even once to show that this is permissible.
As regards how a woman who is in menses would observe I'tikaaf, then the answer is that a woman who is in menses does not observe I'tikaaf because it is not permissible for her to enter the mosque while in menses because the Prophet : "Women in menses should stay away from the mosque." [Al-Bukhari and Muslim]
Finally, it should be noted that if a woman interrupts her I'tikaaf and goes home due to having menses, she will be rewarded for doing so, Allaah Willing, as she is fulfilling the order of her Lord.
Allaah Knows best.