All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It was more appropriate for the enquiring person to marry a Muslim woman to safeguard the religion of his children, though marrying a Christian woman is permissible. Allah Says (what means): {…(Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians)…} [Quran 5:5]
However, you should try your best to call her towards Islam and bring to her knowledge the distinguished features of Islam, and hopefully, Allah will open her heart to Islam. If she embraces Islam, performs the prayer, and becomes free from what annuls her Islam, then she is considered a Muslim woman according to what is apparent for us and we will put her inside matters in the hands of Allah. If she does not embrace Islam and you have to stay with her in a non-Muslim country, then, in this case, you may use coitus interrupts to avoid having children if you fear that they will incline to disbelief.
Allah knows best.