Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question that shows your interest to be stick to Islam’s rulings in your prospective marital life.
Generally speaking, a Muslim man can marry a Christian girl as long as she is chaste. It may also be a good chance for helping her to convert and become a good Muslim woman.
Responding to your question, Dr. Muhammad Salama, PhD in Islamic Studies in English and an Assistant Professor at the Faculty of Islamic Science, Al-Madinah International University, states:
If she is a chaste woman, then you may marry her as it is lawful for Muslims to marry chaste Christian women. Actually, this is a good chance for you to help her to become a Muslim.
Her chastity is a condition as mentioned in the Qur’an, “Moreover, [lawful for you in matrimony are] chaste women from among the believers and chaste women from among those who have been given the Scripture before you- provided you have given them their [full dowry] compensation in marriage- not to commit fornication, nor to take them as lovers.”(Al-Ma’idah 5:5)
Allah Almighty knows best.