Her father thinks that niqaab is mustahabb and tells her not to wear it, but she thinks it is obligatory
Question

                A girl wants to wear niqab, has read the evidence, and believes it to be fardh but her father, who is very religious and practicing, feels that niqab is mustahabb (he has studied all the evidence and based his opinion on this. For his own reasons, perhaps he worries for her safety or doubts her intentions as being sincere, he forbids her from wearing niqab. He does, however, allow that she can wear niqab when she completes her memorization of Surah Baqarah (as he feels that this will prove her sincere), but she worries that this is too long and feels she is sinning by not wearing it. She has tried to demonstrate to her father that she is sincere, but it has not been enough. She does not disobey him because she worries for his health, he has heart issues that make him very ill under any stress and her wearing it against his will would cause him to fall sick. When she tries to bring this up to other women, they feel she is insulting them by implying that they are sinning by not covering their faces, though she does not judge them and tells them she is not trying to force her opinion on any of them and they do not understand because they all feel it is sunnah. What should she do? And because her father believes it is simply sunnah and not fardh, is he obtaining sin from preventing her? Is it haraam for him to do this? And can you give me som daleel for this?.
Praise be to Allah.
    Firstly: 

    It is obligatory for a woman to cover her face in front of 
    non-mahrams according to the more correct of the two scholarly opinions, 
    because of a great deal of evidence that has been explained in the answer to 
    question no. 11774.  

    Secondly: 

    It is not permissible for a girl to obey her father or mother 
    by not covering her face, because there is no obedience to any created being 
    if it involves disobedience towards the Creator. 

    Similarly, it is not permissible for a father to tell his 
    daughter to uncover her face, even if he thinks that niqaab is mustahabb, so 
    long as she is convinced that it is obligatory, because she is obliged to do 
    what she knows and is convinced of, and she will be asked about that on the 
    Day of Resurrection. A person will not move on, on the Day of Resurrection, 
    until he is asked about his knowledge and what he did with it. She will not 
    be asked about her father’s opinion and what he believed. If she does not 
    wear niqaab, then she is disobeying her Lord, so what good will obeying her 
    father do her in that case? 

    The Prophet  (peace and blessings of Allaah be upon him) 
    said: “There is no obedience if it involves disobedience towards Allaah; 
    obedience is only in that which is right and proper.” Narrated by 
    al-Bukhaari (7257) and Muslim (1840). 

    Thirdly: 

    If we assume that it is mustahabb and not waajib for a Muslim 
    woman to cover her face before non-mahram men, neither the father nor anyone 
    else has any right to tell her to uncover her face, because by doing so he 
    is going against the ruling and command of Allaah. How can a Muslim man 
    allow himself to hear the command of Allaah and His Messenger then issue 
    instructions to the contrary, and tell someone not to do what Allaah and His 
    Messenger have enjoined? Allaah says (interpretation of the meaning):  

    “It is not for a believer, man or woman, when Allaah and 
    His Messenger have decreed a matter that they should have any option in 
    their decision”

    [al-Ahzaab 33:36] 

    “And let those who oppose the Messenger’s (Muhammad’s) 
    commandment (i.e. his Sunnah  
    legal ways, orders, acts of worship, statements) (among the sects) beware, 
    lest some Fitnah (disbelief, trials, afflictions, earthquakes, killing, 
    overpowered by a tyrant) should befall them or a painful torment be 
    inflicted on them”

    [al-Noor 24:63]

    The matter is more serious than whether the niqaab is 
    obligatory or mustahabb; the one who forbids what is enjoined by Allaah and 
    His Messenger must re-examine his faith. 

    Just imagine, O you who enjoins something that goes against 
    the command of the Messenger  (peace and blessings of Allaah be upon 
    him), if the Messenger  (peace and blessings of Allaah be upon him) told 
    your daughter to cover her face when you were sitting there, as something 
    that is mustahabb as you believe, and not as something obligatory. Would you 
    go against the command of the Messenger  (peace and blessings of Allaah 
    be upon him) or would you tell her to hear and obey? 

    No believer has any choice but to hear and obey, as Allaah 
    says (interpretation of the meaning): 

    “The only saying of the faithful believers, when they are 
    called to Allaah (His Words, the Qur’aan) and His Messenger (صلى 
    الله عليه وسلم), to judge between them, is that they say: “We hear 
    and we obey.” And such are the successful (who will live forever in 
    Paradise)”

    [al-Noor 24:51]

    What is the difference between the Sunnah of the Prophet  
    (peace and blessings of Allaah be upon him) that is heard directly and the 
    Sunnah that has been transmitted to us via trustworthy men and proven 
    reports? 

    Why would we obey him in the first case and disobey him in 
    the second? 

    Fourthly: 

    If the father fears that his daughter may be harassed if she 
    wears niqaab, and this is a well-founded fear for obvious reasons, such as 
    the Muslim woman living in a place where women who wear niqaab are harassed, 
    there is nothing wrong with him telling her not to wear the niqaab, and in 
    that case she should obey him so as to ward off harm. But if his fear stems 
    from paranoia and worries that are not based on reality, then it is not 
    permissible for the girl to obey him by not wearing niqaab in that case. 

    Fifthly: 

    The girl should try to advise her father and convince him 
    that she has the freedom to choose the opinion that she believes to be 
    correct, whether that is by finding out the evidence for it or by following 
    scholars whom she trusts, and it is not permissible for her, according to 
    sharee’ah, to forsake this opinion because it is not in accordance with her 
    father’s view. Similarly, it is not permissible for him to make her follow 
    his view, and by not allowing her to wear niqaab he is causing her to fall 
    into sin and disobedience, whether that is by not wearing it once, twice or 
    more. Every time she goes out in front of non-mahrams with her face 
    uncovered, she is sinning thereby. 

    Perhaps she can seek the help of people who can convince her 
    father about that. 

    Perhaps it is clear from this answer that this issue is not 
    about convincing her father that wearing niqaab is obligatory. That may or 
    may not be achieved, based on how clear the evidence is and the means used 
    to convince him. Rather the issue that must be focused on is that the girl 
    is not obliged to follow her father’s opinion and it is not permissible for 
    her to forsake what she is convinced of for the sake of his opinion, and it 
    is not permissible for him to make her follow his opinion. There is no point 
    in making her fall into sin until she has memorized Soorat al-Baqarah, or 
    until he is certain of the sincerity of her intentions, for she is sinning 
    every time she goes out without niqaab, as stated above. 

    If the father understands this, and lets her do what she 
    wants, this is what is wanted. If he persists in not allowing her, then the 
    basic principle is that she should not obey him, as stated above. But if she 
    is afraid that he may become sick because of her going against his wishes, 
    then she may uncover her face when she is with him, and cover it when she 
    goes out on her own, without telling him about that. 

    We ask Allaah to help her and make her steadfast. 

    And Allaah knows best.