Maybe Ahsoka gets captured by a dark side cult. They try to convert her by showing her their version of 'justice' through the dark side. They expose her to their cruel and efficient ways of dealing with enemies, which makes her question her Jedi teachings. However, she eventually realizes that their 'justice' is just tyranny in disguise.
A possible plot could involve Ahsoka being betrayed by someone she trusts deeply within the Jedi or among her friends. This betrayal could be so severe that it pushes her over the edge, and she turns to the dark side for revenge. She then uses her newfound dark side powers to seek retribution against those who wronged her.
A great plot could be Ahsoka having to face a Sith Lord who has a personal vendetta against her. This Sith Lord could be an old enemy she thought was dead. Or perhaps a plot where she is training a new group of Force - sensitive individuals in a post - Empire galaxy, and they face threats from remnants of the Imperial forces. Also, a story where she goes on a quest to find an ancient Jedi artifact that has been lost for centuries.
One idea could be Ahsoka getting transported to the DC universe and teaming up with Batman. She could use her combat skills and Force - sensitivity to help him fight against Gotham's villains. Another plot could involve her meeting Wonder Woman and learning about the different types of power and heroism in the DC world. Maybe she gets caught in the middle of a battle between the Justice League and their enemies and has to use her Jedi wisdom to broker peace.
One plot idea could be that Anakin, already on the dark side, tries to convince Ahsoka to join him. He shows her the power that the dark side can offer, like how quickly she could gain the ability to defeat her enemies. But Ahsoka is conflicted as she still has a strong bond with the light side teachings of the Jedi.
One possibility in fanfiction could be that Ahsoka is tricked into the Dark Side. Maybe an old enemy manipulates events to make her feel betrayed by the Jedi Order. This could lead her to explore the power of the Dark Side, believing it to be a way to seek justice on her own terms.
One idea could be a crossover with the Star Wars Rebels crew. Ahsoka could team up with Ezra and Kanan to face a new threat that combines elements from different eras of the Star Wars universe, like a Sith Lord using ancient Jedi artifacts in a new way. Another plot could involve a crossover with the Mandalorian. Ahsoka could cross paths with Din Djarin and Grogu, perhaps helping them in a battle against remnants of the Empire while also sharing her wisdom about the Force.
She might start wearing darker colors. Instead of her usual white and orange, she could don black robes with red accents, symbolizing her new allegiance to the dark side.
One idea could be Ahsoka traveling back in time to the Clone Wars era and changing a small event that has big consequences. For example, she might prevent a key battle from happening which then alters the relationships between the Jedi, the clones, and the Separatists.
The influence of a powerful dark side user who targeted her specifically. This user could manipulate her emotions, play on her insecurities and gradually turn her towards the dark side. They might offer her knowledge or power that she couldn't resist, slowly corrupting her view of the Force.
She might be tempted by the Dark Side if she discovers a hidden truth about the Jedi Order that she can't accept. So she turns to the Dark Side thinking it's a better alternative. For instance, if she finds out that the Jedi have been hiding some dark secrets about the Force, it could push her over the edge.