Is there a sin or culpability upon a girl for refusing marriage at present due to her feeling of psychological unpreparedness and her desire to complete her studies and work?

Marriage is among good deeds and becomes obligatory if one fears falling into temptation, or if one's parents command it. Marriage should not be abandoned for the sake of studies; it may not hinder them but rather aid them, and delay might lead to missing the opportunity for marriage and later regret. The problems others face in their marriages should not be a deterrent; you should strive for a good choice, perform Istikhara, and entrust the matter to Allah.