Her friends like Spencer, Hanna, and Emily would likely be there for her. They've been through a lot together in PLL, so they'd probably offer support and understanding.
Well, it could be about Aria dealing with the new experience while also handling the drama in PLL. Maybe she tries to hide it from the other girls at first because she's embarrassed, and then as the story progresses, they find out and support her.
The plot might revolve around Aria getting sick as a result of all the stress from the Pretty Little Liars' chaos. Her sickness could be a symbol of how the lies and secrets are taking a toll on her. In the fanfic, we might see her struggle with her illness while also trying to figure out who 'A' is. It could be that her weakened state makes her more vulnerable to 'A's attacks or makes her see things in a different light.
It could make Ezra very protective. He might put aside some of his own problems to focus on taking care of Aria. Her friends like Spencer, Hanna, and Emily would also be worried. They might visit her often, bringing schoolwork and gossip to keep her in the loop. But at the same time, they could be distracted from the 'A' mystery, which might put them at risk.
Another potential antagonist could be a new character. Maybe someone who has a vendetta against Aria's friends and is using Aria as a way to get to them. This new character notices that Aria is tired and weak, so they target her specifically, causing more chaos and confusion in the PLL fanfic world.
Perhaps Aria has been working hard on some sort of project in the PLL world, like a school assignment related to the mystery they are all involved in. She's tired but determined. The fanfic could show her friends rallying around her to support her, and together they start to piece together more clues about 'A' as she rests and regains her strength.
Aria's friends could engage her in some relaxing activities. Maybe they could do some yoga or meditation together. This would help her to calm her mind and body. Also, they could offer to listen to her if she wants to talk about what's really bothering her. Sometimes just getting things off your chest can make it easier to sleep.
It could be that Aria's creative mind is working overtime. Since she's an artsy person, she might be constantly thinking about her writing, art, or the various events in the PLL story from an artistic perspective. This over - stimulation of her creative thoughts can make it difficult for her to relax and fall asleep.
Obviously Caroline herself is the main character. Her mother is likely to be in it as well, as mothers often play an important role in a girl's first period experience, like giving advice and support.
It could be about Caroline's initial shock and confusion when she gets her period for the first time. Maybe she's at school and has to deal with the embarrassment of not being fully prepared.