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.
I'm not sure which specific 'Pieck Finger fanfic' is the best. You can try looking on some popular fanfiction websites like Archive of Our Own. There might be a variety of stories there.
Often, there might be themes related to her abilities and how she uses them in different situations. For example, in battle or when facing challenges. Another theme could be her backstory and how it shapes her personality and actions in the fan - created stories.
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.