A woman who is well-known for lying testified that she breast-fed the one who wants to propose to her; should her word be accepted?
Question

                In our family there is a woman who is well-known for lying. When one of my brothers wanted to propose to a girl, this woman claimed that she had breast-fed that girl and that made the boy a mahram to the girl. Does what she said count or is it the case that breast-feeding cannot be proven by the word of a woman who is well-known for lying?
Praise be to Allah.
      The scholars differed as to whether breast-feeding can be 
      proven by the testimony of one woman. The majority are of the view that 
      breast-feeding cannot be proven by the testimony of one woman, and they 
      differed concerning the number required to prove breast-feeding. 

    The Hanbalis are of the view that breast-feeding can be 
    proven by the testimony of one woman. They quoted as evidence for that the 
    report narrated by al-Bukhaari (5105) from ‘Uqbah ibn al-Haarith (may Allah 
    be pleased with him) who said: I married a woman, then a black woman came to 
    us and said: I breast-fed both of you. I went to the Prophet (blessings and 
    peace of Allah be upon him) and said: I married So and so, daughter of So 
    and so, and a black woman came to us and said to me: I breast-fed both of 
    you, and she is lying. He turned away from me, so I came to him from the 
    other side and said: She is lying. He said: “How could you keep her as your 
    wife when that woman has said that she breast-fed you both? Leave her (i.e., 
    divorce your wife).” 

    The more correct view is that of the Hanbalis, that 
    breast-feeding may be proven by the testimony of one woman, because of the 
    hadeeth quoted above, on condition that she be of good character and there 
    are no reservations about her testimony. 

    Ibn Qudaamah (may Allah have mercy on him) said in al-Mughni 
    (8/153): If one woman testifies to breast-feeding, then marriage [of the two 
    who were breast-fed by the same woman] is haraam, if she is of good 
    character. End quote. 

    Al-Bahooti (may Allah have mercy on him) said in Kashf al-Qinaa‘ 
    (5/457): If one woman who is of good character testifies that she breast-fed 
    him five times within the first two years, or a woman of good character 
    testifies that So and so breast-fed him five times within the first two 
    years, or one man testifies to that, then breast-feeding is proven thereby 
    and there is no need for an oath to be sworn by the one concerning whom 
    testimony was given or by the woman who witnessed it, because of the report 
    of ‘Uqbah ibn al-Haarith (may Allah be pleased with him) who said: I married 
    Umm Yahya bint Abi Ihaab, then a black slave woman came and said: I 
    breast-fed both of you. I went to the Prophet (blessings and peace of Allah 
    be upon him) and told him about that, and he said: “How can you (marry her) 
    when she has said that?” And he forbade him to marry her. According to 
    another report he said: “Leave her (i.e., divorce your wife).” Narrated by 
    al-Bukhaari… And the testimony of a woman who is not of good character is 
    not to be accepted. End quote. 

    Based on what is mentioned above, that the view of the 
    Hanbalis is most likely to be correct, with regard to this woman who is well 
    known for lying, her word is not to be accepted when she claimed that she 
    breast-fed that girl, because she is not trustworthy. 

    But we also advise you to be cautious in such matters and to 
    look at the circumstantial evidence. If it is possible that what she says 
    could be true, such as if she had a baby around the time when she claims 
    that she was breast-feeding, and such things were common among you (i.e., 
    women breast-feeding one another's babies), then to be on the safe side, not 
    going ahead with this proposal is a good idea, especially as it is the 
    matter of a proposal, and if the man does not go ahead with it without 
    giving a reason, he is not doing anything concerning which there are shar‘i 
    reservations, and there will be not be any trouble or problems. 

    But if it is the matter of annulling a marriage contract that 
    has already gone ahead, then it should not be annulled on the word of 
    someone like this woman. 

    And Allah knows best.