If your fiancée wears modestly then you may consider her for marriage as long as she has all the qualities that you desire in a marriage partner. The Prophet, peace be upon him, teaches us that the primary criterion to look in a marriage partner is good character and sound religion. Her past experience with hijab may have turned her off. So she cannot be blamed for her fear. So give her time to summon courage to wear it. You may do well, if it poses no problem for you, perhaps to move out to a safer place where there is no such fear. Focusing on fear will only paralyze a person; she should be advised to summon courage. The best way to achieve this is to seek strength from Allah; here is a du’a which I can recommend; it is rightly referred to as the du’a of empowerment:

Hasbiya Allaahu laa ilaaha illaa huwa alayhi tawakkaltu wa huwa rabbu al-arshi al-azheem

(Allah is sufficient for me; there is no god but He; in Him alone I place all my trust; He is the Lord of the Mighty Throne).

It is advisable to read the above du’a three times in the morning after fajr and three times at night before retiring to bed.