Gabi is still alive in the AOT manga. Her fate was determined by the plot and the author's choices, and death wasn't one of them for her in this particular storyline.
It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
Perhaps Sakura is amused by Itachi's unique skills or his way of handling things. Meanwhile, Shisui annoys her because he has a different approach to things that she doesn't like. In the fanfiction, it could be that Shisui is too brash compared to Itachi's calmness, and Sakura, being a fan of Itachi, just can't stand Shisui's antics.
Gabi remains alive in the manga. The plot doesn't lead to her death. It's one of those character arcs where she continues on despite facing various challenges.
Well, one possible fanfiction could be that Gabi and Josh are young and hungry for a new chapter in their lives. When they find out about the pregnancy, it's a mix of shock and excitement. Gabi might be initially scared about how it will change her career plans, but Josh is there to support her. They start preparing for the baby by fixing up a small nursery in their tiny apartment, painting the walls with soft colors and assembling a crib together.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
For a more villainous touch, including Voldemort or his followers could create high - stakes situations. Bellatrix Lestrange could be a terrifying adversary for Harry and Gabi. On the other hand, adding new original characters, like a powerful but reclusive wizard who lives in the Forbidden Forest, could also make the story more exciting.
It could mean that a person who is a fan of 'Attack on Titan' (AOT) is reading or watching fan - created fictional works related to AOT. Maybe they are interested in seeing different interpretations or storylines that fans have come up with.