Well, Vegeta would be a likely character. He might be initially suspicious of the female Goku. Maybe he thinks she's a threat or just can't believe there's another Goku - like being. He could be there to add some comical moments as he tries to understand the situation.
There were a few novels that fit this description, such as Legend of the Earth Emperor, Mountain God in the City, Incense Becomes God, I Actually Became a Mountain God, and so on. You can choose one according to the plot introduction of these novels and your own taste. I wish you a happy reading!
In general, it's a bit of a toss-up. The strength of Manga Goku and Anime Goku can vary depending on the specific arcs and battles. Sometimes, it might seem like one is stronger in a particular situation, but that could change in another.
Jiang Ziya was a historical figure as well as a mythical figure. In ancient Chinese mythology, Jiang Ziya was a famous politician, military strategist, and counselor, and was honored as "Jiang Taigong". Legend has it that he was originally a feudal lord at the end of the Shang Dynasty. Later, due to some reasons, he abdicated and became a civilian. When he met an immortal while fishing, he received the guidance and help of the immortal and became an outstanding politician and strategist. In ancient Chinese novels, the image of Jiang Ziya was often depicted as a god or hero with superior wisdom, superb strategy, and martial arts. He was used as a symbol to inspire people's wisdom.
Another possible main character could be the villain that forces the two Gokus to meet. This villain could be a new, super - powerful threat that the two Gokus need to deal with. Their meeting becomes a crucial part of the story to defeat this powerful foe.
There could also be other characters from the Dragon Ball universe making an appearance. For example, Vegeta might show up. He could be curious about Fem Goku and how she compares to Goku in terms of power. Or Bulma could be there, perhaps she's interested in the technology or biology behind Fem Goku's existence.
Perhaps they would team up against a common enemy. In fanfiction, new threats are often created. They could combine their strength and unique techniques to defeat the bad guy.
Gohan would also be a good choice. As Goku's son, he has his own unique abilities. In a fanfiction, they could enter a father - son gaming tournament. Gohan's intelligence and strategic thinking could complement Goku's brute strength in the game.