Her husband gave her permission to travel for a naafil Hajj then he retracted it; can she travel without his permission?

Firstly: 

What is required of the husband is to fear Allaah in his dealings with his wife and to treat her kindly. If he dislikes one of her characteristics, he should remember that she has other qualities for which he should be pleased with her. He should remember that he too is not free from mistakes and errors, so he should overlook her mistakes and forgive her for her errors if she repents to her Lord. He should treat her kindly so that Allaah may create love and compassion between him and his wife. 

Secondly: 

It is not permissible for a woman to travel for Hajj or for any other purpose except with a mahram, and there is nothing in your question to indicate whether or not there is a mahram with you. If you do not have a mahram to travel with you, then it is not permissible for you to travel, regardless of whether your husband has given you permission or not, even if that is for the obligatory Hajj. 

The scholars of the Standing Committee for Issuing Fatwas said: 

It is established in sharee’ah that it is haraam for a woman to travel without a mahram, because the Prophet (peace and blessings of Allaah be upon him) said, according to the hadeeth of Ibn ‘Abbaas: “No woman should travel except with a mahram.” Narrated by Ahmad, al-Bukhaari and Muslim. And it was narrated that Ibn ‘Abbaas (may Allaah be pleased with him) said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say when he was delivering a khutbah: “No man should be alone with a woman unless she has a mahram present, and no woman should travel except with a mahram.” A man stood up and said: My wife has gone out for Hajj and I have enlisted for such and such a campaign. He said: “Go and do Hajj with your wife.” Narrated by Ahmad, al-Bukhaari and Muslim.

 A woman is forbidden to undertake any kind of travel, unless she has a mahram with her to protect her and look after her. The mahram is her husband, or one to whom marriage is permanently forbidden because of blood ties, breastfeeding or ties through marriage, such as her father, son, brother, brother’s son (nephew), paternal uncle, maternal uncle, father in law, husband’s son, her son through breastfeeding, her brother through breastfeeding, and so on. This applies whether the woman is young or old, whether she is alone or with other women. A group of women is not sufficient in place of a mahram, because of the general meaning of the ahaadeeth, and because the reason (for her not to travel alone) is still there.   

What women and their guardians have to do is fear Allaah and obey the commands of Allaah and His Messenger, and refrain from that which has been forbidden by Allaah and His Messenger, especially when it comes to preserving modesty and chastity and avoiding everything that may lead to evil and corruption. It is not permissible to allow desires for worldly gain to make them negligent with regard to this matter. 

Hence it is not permissible for a woman to travel to perform the obligatory Hajj without a mahram, and those who are in charge of Hajj trips should not allow that, so as to avoid the sin of falling into something that the Prophet (peace and blessings of Allaah be upon him) forbade, and so as to close the door to evil and corruption. Allaah, may He be glorified and exalted, says (interpretation of the meaning): 

“And Hajj (pilgrimage to Makkah) to the House (Ka‘bah) is a duty that mankind owes to Allaah, those who can afford the expenses (for one’s conveyance, provision and residence)”

[Aal ‘Imraan 3:97]

One of the conditions of a woman being able to do Hajj is that she should have a mahram who agrees to make himself available to travel with her, and Allaah does not burden any soul beyond its scope. 

Fataawa al-Lajnah al-Daa’imah (17/334-336) 

Thirdly: 

Just as you should know that it is not permissible for a woman to travel except with her husband’s permission, the scholars are unanimously agreed that it is not permissible for a woman to go for a voluntary (naafil) Hajj except with her husband’s permission.   

Ibn Qudaamah (may Allaah have mercy on him) said: 

As for the voluntary Hajj, he has the right to prevent her from doing it. Ibn al-Mundhir said: All of the scholars from whom I learned knowledge were agreed that he has the right to prevent her from going out for a voluntary Hajj. 

That is because the rights of the husband are obligatory, and she has no right to give precedence to something that is not obligatory. 

Al-Mughni (3/192) 

It is not permissible for you to travel for Hajj –even if you have a mahram – if you husband has retracted his permission. 

But the husband should not prevent his wife from traveling to do an act of worship if that is not for a legitimate shar’i reason; he will have a share of the reward that he attains if he gives her permission, and if he helps her his reward will be greater. 

Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (3/283): If a husband has given his wife permission to do a naafil Hajj, then he has the right to retract his permission before she enters ihram, but if she has entered ihram then it is not permissible for him to retract his permission. 

You have to apologize to your friend and explain to her the reason why you cannot travel with her, and explain that this is obedience to Allaah and seeking not to disobey Him. The Muslim cannot give precedence to pleasing any person, no matter who he is, over pleasing Allaah, may He be exalted. 

We ask Allaah to make things easy for you and to set things straight between you and your husband. 

And Allaah knows best.