Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear questioner, we would like to thank you for the great confidence you place in us, and we implore Allah Almighty to help us serve His cause and render our work for His Sake.
Answering your question, Dr. Mohammad S. Alrahawan, Associate Professor at the department of Islamic Studies in English, Al-Azhar University, Egypt, states:
It is not permissible for a man to marry a woman without the consent of her legal guardian, such as her father or brother either she has or has not previously married.
This is the view of the majority of scholars, including Malik, Ash-Shafi`i and Imam Ahmad. They based their view on report of the Prophet, “There is no marriage except with a guardian.” (Abu Dawud and Ibn Majah)
According to the Hadith of `A’ishah: “And the ruler is the guardian of the one who does not have a guardian.” (At-Tirmidhi, Abu Dawud, and Ibn Majah)
They further based their view on the hadith: “Any woman who gets married without the permission of her gurdian, her marriage is invalid, her marriage is invalid, her marriage is invalid. If her husband has consummated the marriage, then the dowry belongs to her in return for that. If she does not have a guardian then the (Muslim) ruler is the guardian of anyone who does not have a wali.” (At-Tirmidhi, Abu Dawud and Ibn Majah)
In case a guardian prevents a girl from marrying her suitable and qualified match without having a valid and legal reason, guardianship passes immediately to someone who is fit to be a guardian such as the brother or the uncle.
If all her guardians obstruct her from getting married to a suitable match of hers without providing a valid reason, the Muslim ruler should assume the role of her guardian.
This is based on the Prophet’s words, “…If she does not have a guardian, then the (Muslim) ruler is the guardian of anyone who does not have a wali.” The “ruler” here means the judge who governs according to the Shari`ah or an imam of Islamic centers in the West. Therefore, a guardian does not have the right to prevent a woman from marrying any suitor without providing a valid reason.
Allah Almighty knows best.