She changes it a great deal. For starters, the gender difference can bring in a new type of relationship. Instead of the more traditional male - male rivalry, there could be an element of attraction or different kind of respect. Also, her way of handling the Force and Jedi teachings might be different, which would affect how Vader reacts to her.
The presence of a female Obi - Wan completely alters the power dynamic with Vader. Her femininity could be a source of strength in a way that challenges Vader's view of power. She might be more intuitive and use that to her advantage when dealing with Vader. For instance, she could sense his inner turmoil better than a male counterpart. This could lead to her trying to use that to turn him back to the light side in a more nuanced way. Her different physical capabilities might also change the way battles or confrontations between them play out, adding a new layer of complexity to their relationship in fanfiction.
One interesting idea could be a female Obi - Wan being a mentor to a younger generation in a different way than the male Obi - Wan. She might use her unique perspective to train Jedi. As for Vader, a fanfiction could explore his relationship with this female Obi - Wan in a more complex way, like they have a grudging respect for each other's skills.
Their relationship might start with suspicion. Obi - Wan would be cautious as he's seen Vader's evil deeds. But as Vader is suitless and perhaps more 'human' in a sense, Obi - Wan could start to see the Anakin he once knew. This could lead to a slow rebuilding of trust.
Obi - Wan might be shocked at first. His eyes would widen and he'd quickly try to assess Anakin's condition, checking for any visible wounds.
One possible plot could be that Vader, without his suit, is found by Obi - Wan in a hidden location. Obi - Wan, despite their past, decides to help Vader recover. As they interact, they start to understand each other's perspectives better. Maybe they even form an uneasy alliance against a new common enemy in the galaxy.
Perhaps Obi - Wan uses his Jedi skills in a creative way. For example, he could use a Force - related technique that shields Anakin from the influence of the Sith. He might create a sort of Force barrier around Anakin's mind, preventing the dark whispers from corrupting him further.
Often, Obi - Wan uses his mastery of the Force. He might use a Force - push to overpower his guards when they least expect it and then make a run for it. He could also use a mind trick on a high - ranking captor to order his release.
In fanfiction, a female Goku can also change the relationships. The male - dominated friendships and rivalries in Dragon Ball Z could be shaken up. Her presence could make the male characters act differently. For example, Krillin might be more protective of her, or Gohan could look up to her in a different way. This can create new and interesting sub - plots within the story.
The presence of a child would likely make their relationships more nurturing. Female Obi - Wan might take on a more motherly role towards the child, and Anakin and Ahsoka would be influenced by her example. They would become more protective of each other as they are all responsible for the child's well - being.
It creates a power imbalance. Bellatrix is a powerful and cruel Death Eater, and gagging Hermione, who is known for her intelligence and magic skills, gives Bellatrix an immediate upper hand.
Well, in Sherlock and Fem John fanfiction, the dynamic often changes in terms of emotional expression. A female John might be more openly emotional, which can either soften Sherlock or create more tension as he's not used to such displays. Also, the power dynamic can shift. In the original, John was often the more 'grounded' one, but a Fem John might assert herself differently, perhaps more subtly or in a more feminine way.