I really like 'Elena and Rebekah: A New Alliance'. In this fanfiction, an outside threat forces them to team up. The author does a wonderful job of exploring their different strengths and how they complement each other in the face of danger.
A common plotline is them competing for the same guy, which leads to a lot of tension and interesting character development. For example, in some fanfics, they both have feelings for Damon, and this rivalry makes for a very engaging read.
Perhaps she wants Elena to understand her better. Rebekah may feel that Elena has misjudged her in the past, and by sharing her story, she can show Elena her true self.
Their relationship would likely become more intense. With a baby on the way, there's a new level of commitment. Damon might become more tender and less reckless, as he now has Elena and the unborn child to think about. Elena would probably rely on Damon more, trusting him to protect her and their future family.
Well, in such a fanfiction, Elena might befriend Lissy and Josie. Maybe they'd share stories about the supernatural world. Since Elena has her own experiences with vampires, werewolves and witches, she could offer them some unique perspectives. And they could also help Elena adapt to the new environment she might find herself in.
In some fanfictions, there could be a plot where Rebekah and Elena become friends because of their shared experiences with the Salvatore brothers. They might bond over the fact that they both have complex relationships with Stefan and Damon. Rebekah could give Elena some insights into the vampire world from an original vampire's perspective, which Elena finds useful in her own journey.
One idea could be that they face challenges from the vampire and werewolf communities. Since their relationship was already complex in the show, this pregnancy could stir up more trouble. Another plot could be them trying to keep the pregnancy a secret while preparing for the arrival of the baby. They might have to deal with issues like finding a safe place to raise the child in a world full of supernatural threats.
Well, a possible plot is that Elena's pregnancy is the result of a spell gone wrong. Klaus, despite his initial shock, decides to stand by her. This could lead to a series of events where they have to fight off those who see the baby as a threat. It could also explore how Elena deals with the physical and emotional changes of pregnancy while being in a rather strange relationship with Klaus. And the baby might have some unique abilities that are both a blessing and a curse.
Often in fanfiction, their character development is intertwined. As they interact more, they both change. Rebekah might become more empathetic due to Elena's influence, and Elena could become more street - smart in the ways of the vampire world with Rebekah's guidance. Their relationship could shift from one of animosity to one of mutual respect and friendship, which is a significant development for both characters in the Vampire Diaries fanfiction universe.
One possible storyline is that Elena helps Lissy and Josie with a school project related to the history of the supernatural. Since Elena has lived through a lot of it, she has first - hand knowledge. Another could be that they go on a road trip together and encounter various supernatural beings along the way.