Question: All praise be to Allaah Alone, and peace and blessings be upon the Last of the Prophets. To proceed:
The Permanent Committee for Scholarly Research and Ifta’ has viewed the Fatwa that His Eminence, the Grand Muftee, has received from His Eminence the Chairman of Faifa Organization Center: Muhammad ibn `Alee Al-Faifee, under no. 97, dated 16/6/1419 A.H., that was transferred to the Committee from the Secretariat General of the Council of Senior Scholars, under no. 3825, dated 21/6/1419 A.H. His Eminence required the consideration of the Fatwa request that was presented to him by a questioner, to which was attached his letter that reads as follows: To the respected Chairman of Faifa Organization Center, Al-salaamu `alaykum wa rahmatullaah wa barakaatuh (May Allah’s Peace, Mercy, and Blessings be upon you). I present this letter to you so as to tell you that I have a daughter who is 18 years old, and she has a psychological disease. She did not fast 12 days in Ramadaan, 1418 A.H., and whenever she fasted, she had her menstrual period again. Please send my question to the responsible authorities. May Allaah Grant you success. Al-salaamu `alaykum wa rahmatullaah wa barakaatuh.
Answer: After studying the Fatwaa request, the Committee replied that this woman must start compensating for the days that she missed last Ramadaan, by assuming that the duration of her menstruation is the same as the duration that she was used to before the disturbance of her menstruation; so she must spend this period without fasting or offering Salaah (Prayer), and without having sexual intercourse with her husband, if she is married… read more here.