The society in which we live is very demanding and innovate things that are far from what sharia law is. It is very unfortunate that these things have become the part of our ummah. Many girls are not able to get married because they simply and cannot afford the expenses to cover the whole arrangement. Many of our brothers and sisters want to help such poor girls in meeting their expenses of marriage and help them get married. Now the question is, is it permissible?
As a believer we must know and understand that a woman is not obliges to provide or furnish a home. It is a duty of husband to meet these expenses and comes under the heading of maintenance that is his duty towards his wife. In the same way, Mahr is the amount that a husband has to pay to his wife and on that husband has no right. She can use it or part of it to prepare herself.
Regarding wife’s trousseau, the majority of fuqaha are of the view that it is not obligatory for a woman to prepare her trousseau from her mahr or part of it rather it is a duty of husband to prepare the house and everything that is needed for it to be a suitable home.
If girls’ parents or relatives are the ones who spend on her, then it is them who should prepare her for her wedding but if they are not able to do that then it is husband who must provide for it and make it a part of Mahr.
If it a custom in a society to provide for the furnishing of a house such that, without it she cannot get married, then it is permissible to give Zakkah in this case if the parent or guardian is not able to meet the expenses or do not agree to meet it. It is because the need for marriage is greater and genuine, and in some cases it may be like the need for food, drink and shelter.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: If there was a person who can earn enough for food, drink and shelter, but he needs to get married and he cannot afford to get married, is it permissible to give him zakaah funds so that he can get married? The answer is yes, it is permissible to give him zakaah funds so that he can get married and give a full mahr. If it is said: How come it is permissible to give zakaah funds to a poor person so he can get married even if what is given to him is a large amount? We say: Because a person’s need for marriage is a real need, and in some cases it may be like his need for food and drink. Hence the scholars said: If a person is obliged to spend on someone, he should arrange that person’s marriage if he can afford that. So the father is obliged to arrange his son’s marriage if the son needs to get married but he cannot afford to do so. But I have heard of some fathers who have forgotten how they were when they were young and when the sons ask them for help in getting married, they say: “Get married from your own pocket.” This is not permissible and it is haraam if he able to arrange his marriage. His son will dispute with him on the Day of Resurrection if he did not help him to get married when he was able to. Fataawa Arkaan al-Islam, p. 440-441.
Based on this, there is nothing wrong in giving zakat to a person/girl to meet her expenses of marriage.
And Allah knows best.
(Source - Islam Q&A)