It is Allowed For the Suitor to See the Woman to Whom He Has Proposed
Question :
Is it permissible for my sister to veil herself from my paternal uncle's son, who might in the future be her husband, but she is not his wife at present, although we wish to give her in marriage to him, according to the Sunnah of Allah and His Messenger?
Answer:
Yes, it is incumbent upon her to cover herself from her paternal uncle's son and others who are Ajanib (permis- sible for her to marry), even if he has proposed to her, or you have decided to make the contract for him with her.
But it is the right of every suitor who wishes to marry any woman to look at her, without being alone with her, which may lead to his marrying her. As for sitting with him and continually unveiling herself in front of him, and his being alone with her, based upon a promise made regarding her and such like this is not permissible until the contract has been made.
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 5 Pages 199-200