She vowed to do Hajj but she has not done the obligatory Hajj
Question

                A woman vowed that if Allaah blessed her with a child, she would go for Hajj. Allaah has blessed her with a child, but does she have to do Hajj in fulfilment of this vow, knowing that she has not yet done the obligatory Hajj?.
Praise be to Allah.
    It should be noted that vows are not allowed. The Prophet 
     (peace and blessings of Allaah be upon him) forbade them when he said: 
    “They do not bring any good.” Hence some of the scholars are of the view 
    that vows are haraam. Why should you make a vow? Why should you burden 
    yourself? Will Allaah not heal you or your relative unless you stipulate 
    conditions for Him? Subhaan Allaah! Do not make vows, rather ask Allaah for 
    healing. If Allaah wants to heal him, He will heal him whether you make a 
    vow or not. If you do that and you make a vow, if it is a vow to do an act 
    of worship then you are obliged to fulfil it, because the Prophet  
    (peace and blessings of Allaah be upon him) said: “Whoever vows to obey 
    Allaah, let him obey Him.” 

    Based on this, we say to the woman mentioned in the question: 
    You have to go for Hajj, but start with the obligatory Hajj, then do the 
    Hajj that you vowed to do, because it is obligatory for you, and if you do 
    not do it you are exposing yourself to a grave punishment which Allaah 
    mentioned in the verses where He says (interpretation of the meaning): 

    “And of them are some who made a covenant with Allaah 
    (saying): ‘If He bestowed on us of His Bounty, we will verily, give Sadaqah 
    (Zakaah and voluntary charity in Allaah’s Cause) and will be certainly among 
    those who are righteous.’

    76. Then when He gave them of His Bounty, they became 
    niggardly [refused to pay the Sadaqah (Zakaah or voluntary charity)], and 
    turned away, averse.

    77. So He punished them by putting hypocrisy into their 
    hearts till the Day whereon they shall meet Him, because they broke that 
    (covenant with Allaah) which they had promised to Him and because they used 
    to tell lies”

    [al-Tawbah 9:75-77].

    They vowed that if Allaah made them rich, they would give in 
    charity and would be righteous. Allaah gave them that, but they were stingy 
    with the money and turned away from righteousness. “So He punished them 
    by putting hypocrisy into their hearts” – until when? “till the Day 
    whereon they shall meet Him” i.e., until death. “because they broke 
    that (covenant with Allaah) which they had promised to Him and because they 
    used to tell lies.” 

    In conclusion: beware of making vows, and if you do not make 
    vows you will be fine. Do not oblige yourselves to do things that Allaah has 
    not obliged you to do except as the result of your own actions. If a person 
    has a sick loved one, let him say, “O Allaah, heal him.” If he wants to sit 
    an exam, let him say, “O Allaah, grant me success,” because some students, 
    when they find their studies hard and are afraid that they will fail, 
    promise Allaah that they will do various acts of worship if they pass the 
    exams. Then when they pass the exams, they start to ask questions and come 
    to the scholars asking for a way out from the vow, but there is no way out 
    and no other option than to fulfil the vow. End quote.