I'm not sure specifically what a 'catherine cell' is in this context as the term is rather unclear. It could be a very specific or made - up concept within that particular story.
In the 'the black widow the catherine nevin story', Catherine Nevin was probably a person who had actions or a reputation that earned her the 'black widow' title. This could mean she was involved in activities that were not above board. It could be related to financial misdeeds, or actions that took advantage of people's vulnerabilities. Maybe she was at the center of a scandal or a criminal case where her actions were so notable that she became known as the 'black widow' in this particular story.
It could be a mysterious stranger she meets by chance. Maybe at a coffee shop, a guy who strikes up a conversation with her and shows an immediate interest in her life. He could be charming and different from Steve, which draws Catherine to him.
In the context of this fanfic, Catherine Rollins and Steve are likely characters created by the fanfic author. They could be original characters, or they might be based on existing characters from a particular show, movie, or book. Without more context, it's hard to say exactly who they are other than two individuals whose relationship is central to the story where Catherine makes Steve cry.
I'm not sure which specific 'Catherine' in science fiction you are referring to. There could be many characters named Catherine in various science fiction works.
There are those characters from the game who have special powers or unique personalities. For instance, that one character who has the ability to see the future in a hazy way. Including them can bring in an element of mystery. And then there are the characters who are on the fringes of Catherine and Vincent's world but have some knowledge about their relationship, like the old wise man in the alley who gives them cryptic advice from time to time.
Sure, Catherine Palmer is known for being a Christian fiction writer. Her books frequently explore Christian beliefs and their impact on the lives of her characters, which has endeared her to many readers of this specific literary category.