What should a 19-year-old girl do when her parents want to marry her off for various reasons, while she is not interested in marriage and fears being married against her will, and she has already informed them of her unwillingness?

Marriage is part of the guidance and Sunnah of the Prophet, peace and blessings be upon him, and it is not permissible to abandon it for any worldly reason, especially in times of fitan (trials). If a servant fears fitnah for himself, then marriage becomes obligatory for him. A girl should accept a righteous husband and not reject him under the pretext of studying or coveting wealth, so that she does not grow old. It is not permissible to completely disregard marriage, unless the rejection is for a specific person while still accepting the principle of marriage to a suitable match.