If she is afraid that it will be found out that she has become Muslim, how should she pray?
Question

                A non-Muslim girl wants to learn about Islam and testify to Islam in front of Allah. She wants to pray and to do all religious commitments. Is she permitted to pray dhuhr and ‘asr only and leave the other prayers due to the difficulty she will meet at home?.
Praise be to Allah.Firstly: 
We ask Allaah to help and 
    guide this girl and to open her heart to Islam, and to fill her heart with 
    the light of faith. We advise her to do that and not to hesitate, and to 
    announce her Islam to her Lord, and to bear witness to the testimony of 
    Islam, and to do whatever she can of its rituals. 
Secondly: 
The Muslim is obliged to 
    offer the five prayers every day and night, and it is not permissible to 
    omit any of them, no matter what one’s excuse, so long as one is of sound 
    mind. 
If this girl cannot pray 
    Maghrib, ‘Isha’ and Fajr for fear that her family may find out that she is 
    Muslim, then she should not avoid praying, but she can do the following: 

    1-Join Maghrib and ‘Isha’ at the 
    time of the earlier or later prayer, and pray them in secret. Reciting out 
    loud in the prayers in which Qur’aan is recited out loud, such as Fajr, 
    Maghrib and ‘Isha’, is Sunnah, not obligatory. The same applies to raising 
    the hands when saying the opening takbeer and when saying the takbeers when 
    changing posture, and placing the right hand over the left when standing. 
    All of these are Sunnah actions.

    2-She may limit herself to doing 
    the pillars and essential parts of the prayer. So she may recite al-Faatihah 
    and not recite a soorah after it, and she may recite just one tasbeehah when 
    bowing and prostrating. Thus she will be able to do the prayer in a few 
    minutes. Girls are usually able to close the door of their rooms for a few 
    minutes, such as when they change their clothes and the like, so she can do 
    the prayer during that time.

    3-If she wants to do wudoo’, she 
    can do wudoo’ in the bathroom where no one can see her, as if she is 
    relieving herself. If she is unable to do wudoo’ then she can do tayammum, 
    even if she uses the wall or furniture of the house and prays with this 
    tayammum.

    4-If we assume that she cannot 
    hide from her family even for a few minutes in which to pray, and she is 
    afraid that if they find out she is Muslim she will suffer real harm, then 
    it is permissible for her to pray whilst sitting, gesturing for the bowing 
    and prostrating. If that is not possible then she may pray sitting and 
    intending in her heart to bow and prostrate, whilst facing the qiblah. If 
    she is unable to face the qiblah, then she may pray facing in any direction. 
    If we assume that she can only pray whilst lying down, then she may do that. 
    The point is that prayer is not waived for one who is accountable under any 
    circumstances.
The basic principle 
    concerning that is the verse in which Allaah says (interpretation of the 
    meaning): “Allaah burdens not a person beyond his scope” [al-Baqarah 
    2:286] and the words of the Prophet  (peace and blessings of Allaah 
    be upon him): “Pray standing, and if you cannot then sitting, and if you 
    cannot then on your side.” Narrated by al-Bukhaari (1117) and Abu Dawood 
    (952). 
The fuqaha’ mentioned some 
    cases in which the requirement to face the qiblah and bow and prostrate is 
    waived, such as when fleeing from a wild animal or a flood or when fighting 
    breaks out on the battlefield, when there is not enough time to do the 
    prayer properly with all its essential parts. 
Ibn Qudaamah (may Allaah 
    have mercy on him) said in al-Mughni (1/258): To sum up: if the fear 
    is so intense that one cannot pray facing the qiblah or one needs to walk or 
    is unable to do some of the essential parts of prayer, either because of 
    permissible flight from an enemy, flood, wild beast or fire and the like, 
    which one can only escape by fleeing, or when engaging in fighting the enemy 
    or when fighting breaks out on the battlefield, and there is a need to 
    charge and retreat and stab and strike and chase, then he may pray according 
    to his situation, whether he is walking or riding, facing the qiblah if 
    possible, or facing any other direction if that is not possible. 
If he is unable to bow and 
    prostrate, he may gesture to indicate them, and lean forward more for 
    prostration than bowing, according to what he is able to do. If he is unable 
    to gesture, then it is waived. If he is unable to stand or sit and so on, 
    then they are waived. If he needs to stab and strike and charge and retreat, 
    he may do that. He should not delay the prayer until the time for it is over 
    because Allaah says (interpretation of the meaning): “And if you fear (an 
    enemy), perform Salaah (pray) on foot or riding” [al-Baqarah 2:239]. And 
    Maalik narrated from Naafi’ that Ibn ‘Umar said: If the fear is greater than 
    that, they may pray walking, standing on their feet, or riding, facing the 
    qiblah or otherwise. Naafi’ said: I do not think that Ibn ‘Umar narrated it 
    from anyone but the Messenger of Allaah  (peace and blessings of Allaah 
    be upon him). End quote. 
Indeed the fuqaha’ have 
    stated that the prisoner or the one who is afraid that his being Muslim will 
    be discovered should still pray. 
Ibn Qudaamah (may Allaah 
    have mercy on him) said in al-Mughni (2/140): If he flees from an enemy in a 
    permissible sense, or he flees from a flood or wild animal or fire, and he 
    cannot escape it except by fleeing, then he may pray in the manner that is 
    permitted in the case of extreme fear, whether he fears for himself or his 
    property or his family. If a prisoner fears for his life if he prays, or if 
    someone is hiding in a place, then they should pray however they are able 
    to. This was stated by Ahmad with regard to the prisoner. If the one who is 
    hiding is sitting and cannot stand, or he is lying down and cannot stand up 
    or move, then he should pray according to his situation. This is the view of 
    Muhammad ibn al-Hasan. Al-Shaafa’i said: He should pray and repeat it (later 
    on), but this is not correct, because the one who is afraid should pray 
    according to what he is able to do, and he does not have to repeat it, as is 
    also the case for one who is fleeing. It makes no difference whether one is 
    travelling or not, because what makes it permissible is fear of death, and 
    that is the same in both cases. 
Whenever he can find a 
    refuge to do his prayer, such as if the one who is fleeing from a flood can 
    climb to a high place and the one who fears an enemy can enter a fortress 
    where he will be safe from the enemy’s attack and from harm, then he should 
    pray there then come out, and he does not have the right to offer the prayer 
    of extreme fear, because that is only permitted in cases of necessity, so it 
    is only to be done when necessary. End quote. 
To sum up: this girl has to 
    offer the five prayers, and it is not permissible for her to omit any of 
    them. But she may perform the prayer in whatever way she can, which includes 
    offering the prayer of extreme fear if necessary. 
And Allaah knows best.