She did not know that if the menstruating woman becomes pure before Fajr she has to pray Maghrib and ‘Isha’
Question

                I read recently that a woman must pray the previous prayer to the time of when her period stopped, or join two prayers. I did not know this before and I am 38 years old now.
Praise be to Allah.If a menstruating woman 
    becomes pure after the time for ‘Isha’ begins, then she has to pray ‘Isha’ 
    because she was pure during that time. She also has to pray Maghrib because 
    it may be joined to ‘Isha’ if there is an excuse. 
Similarly, if she becomes 
    pure after the time for ‘Asr begins, she has to pray Zuhr and ‘Asr. This is 
    what was stated in fatwas by some of the companions of the Prophet  
    (peace and blessings of Allaah be upon him), and it is the view of the 
    majority of scholars. 
But if she becomes pure 
    after the time for Fajr, Zuhr or Maghrib begins, she only has to offer one 
    prayer, namely the prayer at the time of which she became pure (Fajr or Zuhr 
    or Maghrib), because these prayers cannot be joined to anything that comes 
    before them. 
Ibn Qudaamah (may Allaah 
    have mercy on him) said in al-Mughni (1/238): If the menstruating 
    woman becomes pure before the sun sets, she should pray Zuhr then ‘Asr. 
If she becomes pure before 
    dawn breaks, she should pray Maghrib and ‘Isha’. This opinion was narrated 
    from ‘Abd al-Rahmaan ibn ‘Awf, Ibn ‘Abbaas, Tawoos, Mujaahid, al-Nakha’i, 
    al-Zuhri, Rabee’ah, Maalik, al-Layth, al-Shaafa’i, Ishaaq and Abu Thawr. 
    Imam Ahmad said: Most of the Taabi’een were of this view, except al-Hasan 
    who said that she only has to offer the prayer at the time of which she 
    became pure. This was the view of al-Thawri and ashaab al-ra’y. 
Ibn al-Mundhir narrated 
    that ‘Abd al-Rahmaan ibn ‘Awf and ‘Abd-Allaah ibn ‘Abbaas thought that the 
    menstruating woman who becomes pure one-rak’ah before dawn should pray 
    Maghrib and ‘Isha’, and if she becomes pure before the sun sets, she should 
    pray Zuhr and ‘Asr together. 
Because the time for the 
    second prayer is the time for the first at the time when the excuse is 
    applicable, so when the one who had an excuse no longer has an excuse, then 
    he must offer the obligatory prayer, and he must offer the obligatory prayer 
    for the second prayer too.  
Shaykh Ibn ‘Uthaymeen (may 
    Allaah have mercy on him) favoured  the view that she only has to offer the 
    prayer the time of which she caught up with, and she does not have to join 
    to it the prayer that came before it. 
In order to be on the safe 
    side, you should follow the view of the majority of scholars and offer the 
    two prayers together. But if a woman offers only the prayer the time of 
    which she caught up with, we hope that there is no sin on her. If a woman 
    did not do that in the past because she was unaware of the ruling, she does 
    not have to do anything, because of the general meaning of the evidence that 
    the one who is ignorant and the one who makes a mistake are excused, and 
    because the issue is one where there is a difference of scholarly opinion, 
    as stated above. 
See also the answer to 
    question no. 45648. 
And Allaah knows best.