Should she refuse to go to Hajj because she will go back to sin after Hajj?
Question

I am a young woman, twenty-four years old. I want to go for Hajj, but my relatives told me: You will inevitably fall into sin, such as going to wedding parties, where of course there is music and mixing between men and women.
Therefore, after coming back from Hajj, can I go to places where there is mixing between men and women? Is it permissible for me to go with my paternal uncle for Hajj?
Praise be to Allah.Firstly: 
We would like to congratulate you for your intention and decision to do Hajj, for at this young age, and in that country that is far away, it is very rare to find anyone who thinks of performing this great obligatory duty. Perhaps that is because they are distracted by worldly concerns and eagerness to acquire wealth, and to follow in the footsteps of the people of that disbelieving land. It is for these reasons that Islam advises us not to live among them, and repeatedly warns us against doing that. We ask Allah, may He be exalted, to enable you and your family to live in a Muslim country. 
Secondly: 
You should understand that sins incur the wrath of Allah, may He be exalted, and the one who does them is deserving of punishment. It makes no difference whether those sins occur before or after Hajj. Imam Ibn al-Qayyim wrote in his book al-Jawaab al-Kaafi li man su’ila ‘an ad-Dawa’ ash-Shaafi about a number of the effects that sin has on the one who does it. We have quoted that at length in the answer to question no. 23425. Among the things he (may Allah have mercy on him) said was that sin creates alienation between a person and his Lord, and it is the cause of loss of barakah (blessing), a bad end, things becoming difficult, and scarcity of provision. 
By Allah’s grace towards this ummah, He has ordained for it occasions of good, of which the Muslim may avail himself to expiate his sins and increase his reward. So fasting the day of ‘Arafah bring expiation for two years, fasting the day of ‘Ashoora’ brings expiation for one year, and so on. 
One of the greatest occasions of good and opportunities for doing acts of worship and obedience is Hajj. It is narrated in the saheeh Sunnah that “Whoever does Hajj and does not utter any obscene speech or do any evil deed, will go back as his mother bore him.”
Narrated by al-Bukhaari (1683) and Muslim (1349). 
The wise Muslim takes advantage of such opportunities, not in order to go back to committing sin again after that, but in order to turn over a new leaf and reconcile with his Lord, may He be blessed and exalted. If the Muslim understands that he no longer has any sins on his record, he will give thanks to his Lord, may He be exalted, and part of giving thanks is that he does not go back to doing that which incurs His wrath. This does not mean that the one who does Hajj will never sin again; rather what it means is that it is a characteristic of acts of worship in general that they form a barrier to sin, by the grace of Allah. Another of their characteristics, especially Hajj, is that they take away from a person the consequences and shame of sin. 
For that reason, the Prophet (blessings and peace of Allah be upon him) said: “Make the Hajj and ‘Umrah follow each other closely, for they remove poverty and sins as the bellows removes the dross of iron, gold and silver, and an accepted Hajj brings no less a reward than Paradise.” 
Narrated and classed as saheeh by al-Tirmidhi (810); al-Nasaa’i (2631). Classed as saheeh by Shaykh al-Albaani in al-Silsilah al-Saheehah (2901). 
This indicates that the Muslim may commit sins before and after Hajj, for no one is infallible and immune from falling into sin. But if he does Hajj and ‘umrah a great deal, his sins will be expiated by these repeated actions.
 We do not mean to say that a person has a concession allowing him to sin after Hajj or before it – Allah forbid – not at all. There is no concession whatsoever allowing anyone to disobey Allah. Rather what we mean to say is that if every person who committed a sin refused to go on pilgrimage to the House of Allah, no one would ever go on pilgrimage to the House of Allah, and no one would ever perform the rituals ordained by Allah. 
The same would be true if everyone who was afraid of sin refused to go on Hajj. Pilgrimage to the sacred House of Allah would cease, for there is no believing slave who can guarantee that he will never fall into sin at some point. The most that we can say is: 
Allah has instructed His slaves to repent, as He says (interpretation of the meaning): “And all of you beg Allah to forgive you all, O believers, that you may be successful” [an-Noor 24:31]. 
Part of repenting properly is training oneself not to go back to any of that sin, minor or major. If one is overcome by one’s nafs and goes back to any of that sin, then he must hasten to repent once more, and to do a lot of good deeds. 
Falling into sin requires us to hasten to do acts of worship and obedience, and to do a great deal of such acts at all times and on all occasions, not to neglect a significant act of worship, such as pilgrimage to the sacred House of Allah, for fear of falling into sin once more. This is contrary to the nature of things. 
Thirdly: 
With regard to going with your paternal uncle, yes it is permissible for you to go with your paternal uncle, because he is one of your mahrams. If this is the obligatory Hajj, then going with him is obligatory for you, not merely permissible. 
So seek the help of Allah and hasten to do Hajj, and strive hard to repent to Allah and express your need for Him to protect you from sin and error. 
And Allah knows best.