Is it permissible to marry a repentant fornicator who desires chastity, knowing that she is 19 years old and living in difficult circumstances?

Adultery is one of the gravest sins, and circumstances do not justify it. Taking a life is an even greater sin. The woman must make sincere repentance and turn to obedience to Allah. Allah transforms evil deeds into good deeds for those who repent. There is no objection to marrying her after her repentance is confirmed. You must sever the illicit relationship with her, and if you wish to marry, contact her guardian.