No. Fanfic that involves sexual content is often inappropriate and goes against ethical and moral standards. It can also make others uncomfortable and may not be suitable for public consumption or within the context of a respectful fan community.
One way is to have strict community guidelines. Fan communities can clearly state that any form of sexual fanfic is not allowed. Moderators should be vigilant and remove such content when they find it.
Alexis might confront Beckett directly. She could say something like 'I think you're cheating on me. What's going on?' This is a very straightforward approach.
It's not okay. Ruby Rose is a real individual, and creating such fanfic goes against respecting her as a person. We should focus on positive and respectful ways to engage with her work or public image, like discussing her acting roles or contributions to the entertainment industry.
A lawyer could be an important character. This lawyer takes on Alexis's case, believing in their innocence. The lawyer has to battle a corrupt legal system or powerful opponents who want to see Alexis locked up for good. The fanfic could show the lawyer's strategies and how they build a case in Alexis's favor.
Spreading or seeking out sex stories about someone is unethical and a violation of privacy. We should respect others' dignity and focus on their positive contributions like their work in the fashion or entertainment industry.
You could write an adventure - based fanfic where Summer Rose goes on a heroic journey. Describe her battles, her growth as a character in terms of courage and wisdom, rather than involving sexual elements.
Perhaps there have been some rumors or whispers in their fictional world that have reached Alexis' ears. Even if they are baseless, they can plant the seed of doubt in Alexis' mind, making her think that Kate is cheating.
She could be defensive of Beckett. Since Alexis probably has a good relationship with Beckett, she may try to convince Castle that he's wrong and that Beckett didn't mean any harm. For example, she might tell Castle about all the positive things Beckett has done for her.