Nami is the child of Celestial Dragons who was imprisoned by a Fishman, who mimicked the CDs by taking humans as slaves and calling them inferior to Fishmen.
This is foreshadowed by her being connected to royalty (is close with multiple princesses, while also sharing their faces, almost as if they're all related going way way back), being lauded for her beauty, her obsession with money and thievery (the CDs are greedy thieves), and being seen as the Pirate King, Luffy's, right hand woman, standing beside him to take down a fake God, Enel.
Skypiea is a real god (Luffy) and a fake god who is royalty (Nami) defeating a fake God who reigns destruction down from above (Enel foreshadowing Imu).
So, let's look at the Celestial Dragons. Do any of them resemble Nami? Bingo, this crazy racist chick right here:
I've thought Nami would rescue Arlong from the CD's for a while, but this works perfect.
Just like Sanji was kidnapped by Royalty he despised, the Germa, after having his backstory hidden, Nami will be kidnapped by the WG and declared a Celestial Dragon. This will lead to Nami meeting Arlong, who is enslaved by her evil sister, Shalria (fuck this lady, when I tried to Image Search all I got was Shakira pics. Which, I mean, damn, Shakira is sexy and awesome, but, that's NOT what I was looking for).
The Celestial Dragons have actually been shown to care about each other significantly. Once Shalria realizes Arlong enslaved Nami, she'll give Arlong to Nami as her own personal Fishman slave. Except, Nami will try to free him, or at least take care of him, rather than abuse him.
Alrong being protected by the Celestial Dragon, a girl he abused and enslaved, will make him realize that Otohime was right: humans can be good. Even a Celestial Dragon can choose to be a good person, and reject all the power in the world, to help a slave, just for the sake of helping someone.
Nami will become Queen of the World once Imu, her mother/great great great great etc. grandma, is defeated, while Luffy will "rule" the oceans as King of the Pirates.