Highlight the female characters' intelligence and skills. If the fanfic had a scene where a girl was being put down in a council meeting, rewrite it to show her outsmarting her opponents. She could present a brilliant strategy or solution that makes everyone respect her. Instead of her being the target of ridicule, she becomes the center of admiration for her capabilities.
Remove any elements of degrading language or actions. Replace them with positive interactions and support. For instance, if a girl was being physically harassed in the fanfic, rewrite it so that other characters, male or female, come to her defense. Then, have her take part in activities that build her confidence, like training in combat or learning a new language, to show that she is in control of her own growth and development.