Well, they're sisters. Alison was sort of the 'dominant' one in their relationship. Courtney had her own issues and was in and out of places like mental institutions. Alison, on the other hand, was the 'queen bee' in their town. Their relationship was full of secrets and lies, which was a big part of what made the 'Pretty Little Liars' story so interesting.
It was Sasha Pieterse. She did a great job of differentiating between Alison and her twin, even though they were played by the same person. She was able to show different personalities and mannerisms for each character, which was really impressive.
The existence of Alison's twin added a major twist to the story. It explained some of the strange appearances and disappearances that had been confusing the other characters. It also brought in new layers of mystery and danger as the twin had her own motives and secrets.
One major event was when Courtney tried to take Alison's place in their social circle. Also, there were events related to their family secrets. Their relationship was a key part of the mystery in the show.
There are fanfictions where Alison's cousin has a secret past related to the 'A' mystery in Pretty Little Liars. In these stories, the cousin's actions can either help or hinder the Liars as they try to figure out who 'A' is. For example, the cousin might be unknowingly working for 'A' at first but then has a change of heart.
One common theme is love and redemption. Their relationship in the show had so many ups and downs, and in fanfiction, often they are exploring how to truly love each other and redeem themselves for past mistakes. Another theme is mystery, as they still have to deal with the secrets of Rosewood even in their relationship.
One interesting scenario could be Alison and Emily going on a secret adventure together, away from all the drama in Rosewood. They might discover a hidden place in the woods that has a special meaning for their relationship.
Well, obviously Alison herself is always interesting. In fanfiction, her character can be explored even more deeply, especially when her cousin is involved. Her cousin can also be a very interesting character. Depending on how the author writes them, they could have unique personalities and motives that add to the overall intrigue of the story.
One interesting moment could be when they team up to solve a mystery in the fanfiction world. Maybe they find a clue that no one else has noticed and it deepens their friendship.
One plot idea could be Alison trying to keep her pregnancy a secret from the other liars at first. Maybe she's afraid of how they'll react or she doesn't want to involve them in her mess. Another could be exploring who the father is and the drama that unfolds as she tries to figure that out. It could also be about her dealing with the physical and emotional changes of pregnancy while still being in the middle of all the mystery and danger in Rosewood.