One possible plot is that the baby's father is someone unexpected. And Rachel has to deal with the reactions of her friends and family. She might also face challenges in her career because of having a baby at a certain point in her life. For example, some directors might be hesitant to cast a new mother. But Rachel, being the determined person she is, tries to prove that she can handle both motherhood and her acting career.
It could be an overzealous security guard. If Rachel was at a high - profile event and the security guard misinterpreted her actions as something threatening or against the rules, he could be the one to call the cops and get her arrested.
It could lead to a major shift in the story and dynamics among the characters. Maybe the other characters would struggle to cope with the loss and it could change the entire tone of the fanfiction.
Finn could be involved if the fanfiction wants to explore a relationship with him as the possible father. He was an important part of Rachel's life in the original series, and his reaction to the news would be significant.
There are many possible fanfictions on this topic. One could be where Rachel is bullied for her over - the - top ambitions in the Glee club. Maybe some of the other members are jealous of the attention she gets from the teacher and start to spread rumors about her, which makes her feel isolated.
There are probably 'Rachel Berry fanfiction' stories that focus on her relationships. For example, a story could explore her relationship with Finn in an alternate universe where things turned out differently. It could show how they might have overcome more challenges together and grown even closer.
Family and friendship dynamics are also common themes. The baby affects not only Rachel but also her relationships with others. Her friends might have different reactions to the new addition to her life, and her family could either be very supportive or create some sort of drama. This all makes for interesting storytelling within the 'Rachel has a baby fanfiction'.
I'm not sure about the absolute best, but some popular authors in the Glee fanfiction community might be good places to start. You could look for authors who have a high number of views and positive reviews on fanfiction platforms. For example, some authors who have been writing Glee fanfiction for a long time and have a deep understanding of Finn and Rachel's characters are likely to create great stories.
Perhaps in the fanfiction, Rachel is wrongly accused of stealing a valuable prop from the theater. She was just borrowing it for inspiration but there's a misunderstanding and she ends up getting arrested. Then she has to fight to prove her innocence.