Can an Egyptian Muslim woman marry a Lebanese Muslim man who lives in Saudi Arabia? And what if her mother doesn't agree on their marriage only because of the different nationalities and because she wants her daughter to live in Egypt? knowing that the daughter is 21 years old and her father died since she was only 2 years old..

Dear honorable sister,
Marriage issues require taking into account the social status and compatibility between spouses. One must not be hasty in making a marriage decision; rather, one should consult family members and learn from their life experiences. In fact, marriage is not a picnic; it includes responsibilities, a family that needs expenses, and independence from others. It is an important matter that should not be taken superficially and should not be based on mere admiration; rather, it is a continuous life relationship, and affinity necessitating social, intellectual, environmental, and cultural harmony between spouses. Therefore, making a decision based on first impressions is of no consequence. A mother possesses experience in life, always seeks what is best for her daughter, and strives to give her to a reliable husband. Allah has instilled the innate feelings of motherhood into a mother's heart and commanded daughters to consult their mothers; it has made her advice a kind of protection for her daughter in the matter of marriage. Therefore, it is fundamentally obligatory for a girl to follow her mother's advice in this respect.
Shari'ah (Islamic law) waived the obligation to obey a mother in this respect only when she refuses a suitor for the sake of objection. Based on this, you should seriously heed your mother's advice and discussions. However, you are the one who will make the final decision, because it is you who will marry and bear the consequences of your decision; a mother is only a trustworthy advisor.
Know that Islam does not discriminate between people except through piety. However, Islam takes into consideration differences in customs and traditions. Therefore, scholars discussed the matter of spousal compatibility to guarantee the stability of marital life, and the endurance of love between spouses in particular and between their families in general.
Declining a marriage request due to a difference in nationality is not always deemed an injustice. This is because just as Islam takes into account compatibility between spouses to protect a woman from enduring living standards she is not used to, it takes into consideration customs and traditions which differ from one country to another. However, some customs and traditions may be different while others may be similar.
A mother seeks what is in the best interest of her daughter due to the innate feeling of motherhood that Allah has instilled in her heart. This, together with her life experiences, gives her the ability to choose well for her daughter. On the other hand, a daughter does not consider anything of such matters, her consideration of interests revolves only around her wish to marry a certain man. Therefore, your mother's objection to marry the person of your choice is not deemed an injustice as much as it is an innate concern over your interests. A mother is commanded to advice her daughter with respect to choosing a good and generous husband who will make her happy.
Based on this, you should follow your mother's advice since she is able to decide on what is in your best interest and brings you happiness in your marital life. Your mother is entitled to choose a good husband for you who fears Allah.
May Allah amend your affairs and grant you success in that which you love and pleases you.