What is the ruling on a mother refusing to marry off her daughter to a young man whom the daughter loves for the sake of Allah, and to whom she has been engaged three times, under the pretext of her young age and the suitor's study abroad, knowing that their acquaintance occurred online?

The relationship with the young man must be severed until a legitimate marriage takes place, for any relationship before that is a snare from Satan. The woman can strive to convince her family of the marriage through the mediation of relatives, and she should not remain silent for fear of falling into temptations that displease Allah.