Marriage is invalid without a Waliy, as it leads to great evils. It was authentically reported that the Prophet (peace be upon him) said:
"There is no marriage without the permission of a Waliy."
Asking the suitor to wait until the girl finishes her studies is something that depends on their agreement. It is better for them to hasten to conclude the marriage contract as long as they can afford to do so. This is because the Prophet (peace be upon him) said:
"O young people! Whoever among you is able to marry should do so, for marriage would help him lower his gaze and keep his virtue. Whoever is not able to marry is recommended to observe Sawm (Fast), for Sawm would alleviate his sexual desire."
A girl should obey her parents in matters that are good. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.