All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Marriage without having the consent of the guardian of a woman is not valid.
The Prophet said: “Any woman who married without the consent of her Wali (guardian), her marriage is void, her marriage is void, her marriage is void.” [Ahmad]
Therefore, every woman who marries without the consent of her guardian should be separated from her husband. After observing her Iddah (waiting period) she may get married with him fulfilling all the conditions of a valid marriage. The guardian of this woman may reject marrying him if he is not suitable for her. If he is religious and has a good moral conduct, then the guardian is not permitted to refuse him.
The Prophet said: “If a man whose religion and moral conduct are pleasing to you proposes to you, let him marry; otherwise there will be great mischief and corruption on earth.” [At-Tirmithi]
Know that the difference of countries is not a legal excuse to reject marrying a religious and a noble person.
Moreover, parents are always more kind than others to their daughter. So, it is most likely that they don't reject any proposal but for a good reason. Therefore, a daughter should obey them unless it is proved that they do not want to marry her by frequently rejecting the good proposals. In this case, she can take her matter to an Islamic court or whoever may act instead, such as Islamic Centers to marry her off.
Allah knows best.