Is it permissible for the fiancé to prevent his fiancée from traveling without a mahram, and from speaking to certain men, especially since her guardian does not prevent her from doing so, and she believes that she is not obligated to obey him, but only to inform him?

The suitor has no right to prevent his fiancée from traveling without a mahram, as the matter rests with her guardian, who must fear Allah concerning her and prevent her from forbidden acts. I advise her of the necessity to adhere to Islamic law and to obey her husband once the legitimate marriage contract is concluded.