What should a girl do who was raped by someone to force her to marry him, and she hates him? And is her marriage valid if she is coerced into it to preserve her reputation?

The questioner did not clarify the nature of the coercion into marriage. If it was merely moral pressure, it does not constitute legitimate coercion, and the marriage is valid if it fulfills the conditions. However, if her guardian forced her, the matter requires further detail. It is not permissible for a fornicator to marry the one with whom he committed fornication unless there is repentance and a period of 'istibra' (waiting period to ensure no pregnancy). If the marriage occurred before these, it is valid according to some jurists. We also note that rape often occurs due to a woman's laxity in being alone with men.