I know many think that Rose is Pink Diamond, but my theory is that Rose was actually the "daughter" of Pink Diamond, maybe even the first Gem born on Earth after Pink Diamond began colonizing it thousands of years ago. Due to the properties of Earth, Rose was born more free spirited then most other Gems. It's likely all Earth-born Gems carried this trait (look at Amethyst), but being the first, she held favoritism and privilege, which would explain why she had so many gardens and secret places of her own, and likely lived a mostly care-free life for the first part of the colonization.
At some point, Rose's outlook influenced the mindset of Pink Diamond herself, who returned to Homeworld to inform the other Diamonds that she was going to end the Earth Colony to preserve the planet, as there was something greater about it that they had yet to explore. Considering they wanted it to be a mass produced Kindergarten Colony, the other Diamonds disagreed, and shattered (or maybe imprisoned) Pink Diamond, removing her from the Authority and sending Blue Diamond to finish the conversion. When Rose learned of what happened, she started the rebellion to save Earth and avenge her "mother", with Pearl attaching to her due to the loss of her Diamond. All the other earth-born Gems joined with her, as they held the same connection to the planet that she had, plus any converts (like Bismuth, and later Garnet).
I mean, it makes more sense to me, since Rose isn't a diamond (not the shape or quality), but is obviously not a "run of the mill" Gem either, she is the only Quartz (aka warrior) that has a shield rather then a regular weapon, Bismuth has to make her a weapon for her to fight in the Rebellion. I have a feeling she was actually the first (and only) of her kind, all due to her birth thousands of years ago when the planet was young and unspoiled.