Is it permissible for me to sit with my fiancée, in her full hijab and in the presence of her family, to learn about her character and traits before completing the marriage, for fear of a difference in character that could lead to divorce in the future?

The Islamic ruling regarding the pre-marital viewing for the suitor and the fiancée aims at knowing the physical appearance, not the character. Acquiring knowledge of character and morals requires a long companionship or travel, and even then, many people feign and display their best while concealing their worst. Therefore, illicit relationships during the engagement period do not achieve the goal of knowing one's character. Rather, both parties should inquire about the other's character from those who know them and have lived with them, and consult people of sound judgment, while seeking out religiosity and Islamic morals. This suffices over other matters.