It is not permissible for a Muslim woman to marry a kaafir, and the marriage is not valid.
Allaah says (interpretation of the meaning):
“And give not (your daughters) in marriage to Al‑Mushrikoon[polytheists] till they believe (in Allaah Alone)”
“O you who believe! When believing women come to you as emigrants, examine them; Allaah knows best as to their Faith, then if you ascertain that they are true believers send them not back to the disbelievers. They are not lawful (wives) for the disbelievers nor are the disbelievers lawful (husbands) for them”
The fact that she was forced into that does not justify her giving in and surrendering to this marriage. The Prophet (peace and blessings of Allaah be upon him) said: “There is no obedience to any created being if it involves disobedience to the Creator.”
This marriage is regarded as invalid, and intercourse with him is zina (fornication, adultery). End quote.