Her father forced her to get married; is this marriage valid and what is the ruling on intercourse in this case?
It is haraam for the guardian (wali) of the woman to force her to marry someone she does not want and does not like, because the Prophet (blessings and peace of Allah be upon him) said: “The virgin should not be given in marriage until her permission has been sought.” Narrated by al-Bukhaari, 6968; Muslim, 1419.
The apparent meaning is that this is general and applies to every virgin and every guardian; there is no difference between a father or any other guardian, hence al-Bukhaari interpreted the hadeeth by saying: “Chapter: The father or other guardian should not give a virgin or previously married woman in marriage except with their consent.”
The woman’s guardian has to fear Allah with regard to his daughters and not give them in marriage to anyone except those with whom they are pleased from among men who are compatible and suitable. The guardian should only give her in marriage for her interests, not for his own.
Shaykh al-Islam Ibn Taymiyah said: With regard to giving her in marriage when she is reluctant, this is contrary to the basic principles and common sense. Moreover Allah did not allow her guardian to force her into buying or renting without her permission, or to eat or drink or wear something that she does not want, so how can he force her into sleeping with and living with someone she does not want to sleep with, and living with someone she does not want to live with.
Allah wants love and compassion between the spouses, and how can that be attained when she hates him and does not like him? What kind of love and compassion can there be in that case?!
End quote from Majmoo‘ al-Fataawa, 32/25
If the marriage contract has been done even though she was reluctant, then this marriage contract depends on the woman’s decision. If she accepts it, then it becomes a valid marriage contract, and if she does not then it is an invalid contract.
It was narrated that Buraydah ibn al-Haseeb said: A girl came to the Prophet (blessings and peace of Allah be upon him) and said: My father married me to his brother’s son so that he might raise his own status thereby. The Prophet (blessings and peace of Allah be upon him) gave her the choice, and she said: I approve of what my father did, but I wanted women to know that their fathers have no right to do that.
Narrated by Ibn Maajah, 1874. It was classed as saheeh by al-Buwaysiri in Masaabeeh az-Zujaajah, 2/102. Similarly Shaykh Muqbil al-Waadi‘i stated: (It is) saheeh according to the conditions of Muslim. End quote from as-Saheeh al-Musnad, p. 160
In the event that the woman does not accept this marriage, then it is invalid and she has to tell the one who did this marriage contract with her about that. He does not have the right to force her to engage in intercourse and intimacy, and she does not have the right to allow him to do that so long as she does not accept this marriage.
Although the ruling on this marriage is that it is invalid, this ruling cannot be proven or established unless the man divorces her by talaaq or the court issues a ruling to that effect, because of the difference of opinion among the scholars concerning the validity of such a marriage; many scholars regard this marriage as permissible.
Based on that, you have to refer the matter to the Islamic judge (qaadi) to pass a verdict that this marriage is annulled.