What is the ruling of Sharia on marrying a minor girl without the permission of her guardian (who refuses the marriage because the suitor is already married), and is it permissible for one of her relatives to marry her off if her guardian continues to refuse?

The father has guardianship over his daughter's marriage (wilayat al-nikah). This guardianship is not removed from him except in the case of 'adl (obstruction), meaning when he prevents his daughter from marrying a suitable suitor. In such a case, the ruler (sultan) or his representative intervenes to compel the father to marry off his daughter, or he himself marries her off, or the guardianship is transferred to another guardian. It is not permissible for a suitor to take the girl without the knowledge and consent of her guardian, as this constitutes an assault on a Muslim's honor and a severing of kinship ties. However, the girl can present her case to the Sharia judge to marry her to the suitor if he is suitable.