No, it is not appropriate. Gwen Stacy is a character from various fictional universes, and creating sexual fanfiction about her is disrespectful to the character and goes against ethical and moral standards in fan communities. Fanfiction should focus on positive, creative, and respectful interpretations of characters rather than sexualizing them.
You could write action - packed fanfic. For example, create a story where Gwen Stacy teams up with other superheroes to fight a powerful villain. This would focus on her skills and bravery.
Peter Parker is one of the main characters. He has a deep connection with Gwen. Her father is also important. He's often concerned about Gwen's safety in the dangerous world of the comic. And there are the villains like the Green Goblin who play a major role in the story.
In certain comic continuities, Gwen Stacy is alive. However, her status has changed throughout different comic arcs and reboots. Sometimes she's been brought back through various means in the fictional comic world.
Gwen Stacy is not trans in the comics. The character has been presented in a conventional gender role throughout the comic series. There have been no storylines suggesting otherwise.
Gwen Stacy was an important figure in the Spider-Man comic universe. She was smart, kind, and had a complex relationship with Peter Parker. Her death had a huge impact on the story.
One of the best Gwen Stacy stories is in 'The Amazing Spider - Man' issues where her relationship with Peter Parker is explored. It shows their sweet and sometimes tumultuous relationship, and how Gwen was a strong - willed character in her own right.