One interesting fanfiction could be where the Gilbert sister discovers a hidden power within herself that links her to the vampire world in a unique way. Maybe she has the ability to see the true nature of vampires, even when they are using their compulsion. This could lead to all sorts of interesting plot twists as she gets involved with the main characters of the show.
One common theme is her struggle to fit into the world that has been turned upside down by the presence of vampires. She often has to deal with the danger that vampires pose to her and her loved ones while also trying to understand their complex nature.
Elena Gilbert in the 'Vampire Diaries' novel is a key figure. She's a typical yet extraordinary high - school girl at first. Typical in the sense that she has the normal concerns of a teen like friendships and school, but extraordinary because she gets pulled into the vampire realm. Her beauty and charm attract the attention of many characters, especially Stefan and Damon, which leads to a lot of drama and action throughout the story.
One common theme is loyalty. Sisters in the fanfiction often show unwavering loyalty to each other despite the supernatural challenges they face. Another is sacrifice. They might be willing to sacrifice their own happiness or safety for their sister. For example, in many stories, a sister will put herself in danger to protect her sibling from a vampire or a witch's curse.
In Vampire Diaries fanfiction, the concept of a twin sister sacrifice can add a whole new layer of drama. It could be related to some dark magic ritual where a twin's sacrifice is needed to gain power or break a curse. For example, perhaps a powerful vampire or witch demands it to achieve immortality or to control the supernatural elements in Mystic Falls.
One common theme is family loyalty. The sisters often have to stick together in the face of the many threats in the vampire - filled world. Another is power struggles. The sisters may have unique powers that others want to control or use for their own gains.
One important plotline is her relationship with Stefan. They fall in love, but their relationship is complicated by Stefan's vampire nature. Another is her encounters with Damon, who also has feelings for her. Her transformation into a vampire later in the series is also a major plotline.
Love is also a common theme. It could be romantic love for her character or platonic love within the family. In some fanfictions, Klaus's sister falls in love with a character from the show, and this love story is intertwined with her relationship with Klaus. For instance, in 'Love and Blood', her love interest is a werewolf, which creates a lot of drama considering the vampire - werewolf dynamic in the Vampire Diaries.
You can also explore the impact on the relationships within the Vampire Diaries universe. Maybe the sister was in a relationship before the amnesia. Now, her partner has to deal with her not remembering their love. It could lead to some really interesting plot twists, like the partner having to fall in love with her all over again while she discovers new aspects of herself.
A common plotline is the sister's adjustment to the new world she's come back to. Things might have changed a lot since she died, like new vampire lords or different witch covens in control.