You could introduce some conflicts or mysteries. For example, strange noises coming from the attic or a locked room that she feels compelled to investigate. As for the plot, perhaps she finds a clue that might lead to her escape, but it's not easy. She has to face her fears and solve puzzles along the way.
One idea could be that Bella discovers a secret passage in the school while locked in. She's scared at first but her curiosity gets the better of her. As she explores, she uncovers some long - forgotten secrets about the school's history.
One possible fanfiction could be that Bella is caught in a sudden and violent snow storm while on a hike in the mountains. She's scared as she realizes she's lost her way and her phone has no signal. The cold is seeping into her bones and she starts to hallucinate about strange creatures in the snow. But then she remembers some survival skills she learned before and starts to build a snow shelter to wait out the storm.
Well, in some fanfictions, Bella might be scared of Edward because of his vampiric nature. His superhuman strength and speed could be intimidating. Also, the unpredictability of his actions as a vampire who is constantly fighting his bloodlust could make Bella feel scared.
One way the story could develop is by introducing a character who helps Bella overcome her fear. For example, a kind neighbor could notice Bella's distress during a thunderstorm and offer her comfort. They might start spending time together during storms, and gradually Bella becomes less afraid.
He could be a bit confused at first. Maybe he doesn't fully understand why Bella is so scared. But then he would likely start to take steps to ease her fears. He might open up to her more about their relationship and what it means, so that she feels more in control and less frightened.
Well, perhaps Bella is in a small town during a snow storm. She's staying at an inn and hears rumors of a ghost that haunts the town during such bad weather. As the snow storm intensifies, she starts to see strange shadows outside her window. She's so scared that she barricades herself in her room. Later, she finds out that it was just a prank by some local kids who like to play on the fears of tourists during storms.
One common theme could be redemption. If Bella is in a broken and scared state, she might be on a journey to redeem herself or find her place again. Another theme could be survival, as she tries to get through whatever has made her broken and scared.
A secret organization could be the antagonist. They might see Bella as a threat to their hidden agenda. For instance, if she has stumbled upon some information about their illegal activities, they lock her in a room to keep her silent and prevent her from sharing what she knows with the outside world.
Perhaps it's a more romantic take. Bella could be locked in a room by a love interest who is too shy or conflicted to face her directly. So, in a rather clumsy way, they lock her in a room with the intention of finally confessing their feelings but are struggling to find the right words.
To write a Tim Drake Scared Fanfiction, you can also focus on his relationships. Maybe he's scared of losing someone close, like Batman or another member of the Bat - family. Build the story around that fear. You can show his fear through his actions, like fidgeting, looking over his shoulder constantly. And don't forget to have a good plot structure. Have a clear beginning, middle, and end. The middle part should be where the fear intensifies, like he discovers more and more about the threat.