If her period comes when she is junub, should she still do ghusl for janaabah?
Question

                How should a woman purify herself from janaabah when she is menstruating? If she purifies herself from janaabah when she is menstruating, should she do wudoo’ and take three handfuls of water then wash her right side then her left side? Or should she just wash herself without doing wudoo’ because she is also menstruating? Is she cleansed of janaabah and is only menstruating, or what?.
Praise be to Allah.
    If a menstruating woman becomes junub, or she is junub and 
    her period begins, it is prescribed for her to do ghusl to cleanse herself 
    from janaabah. The point here is that she will then be able to recite 
    Qur’aan without touching the Mus-haf, because the one who is junub is not 
    allowed to touch the Qur’aan, unlike one who is menstruating. See question 
    no. 2564 and
    60213. 

    The way in which this ghusl is done, as in all other cases 
    prescribed by sharee’ah, is to start by washing the parts of the body that 
    are washed in wudoo’, then pour three handfuls of water over the head, then 
    wash the right side then the left, then pour water over the whole of the 
    body. Thus janaabah is removed but menstruation remains. 

    Ibn Qudaamah (may Allaah have mercy on him) said in 
    al-Mughni (1/134): If she does ghusl from janaabah at the time when she 
    is menstruating, her ghusl is valid and the ruling on janaabah no longer 
    applies to her. This was stated by Ahmad who said: The janaabah is removed 
    but the menses is not, until the flow of blood ceases. He said: I do not 
    know of anyone who said that she does not have to do ghusl except ‘Ata’, but 
    it was also narrated that he said that she should do ghusl. End quote. 

    And Allaah knows best.