Commentary for Kiddushin 91:3

Rav resolves the difficulty raised on R. Assi. The baraita could refer to a case where the man seduced her not for the sake of marriage, but just for sex. In this case, there never was a betrothal, so of course she can refuse the marriage.

Obviously, if he seduced her without the intent of marriage, then she is not married. The rabbis do not believe that premarital sex causes a marital bond. So then why would we even need this verse? R. Nahman b. Yitzchak argues that the verse is necessary to teach that he pays the fine, even though she refused to subsequently get married and her father consented to the marriage. Without this verse we might have thought that he pays the fine only if the father refuses the marriage, not she.