Gems aren't humans. In many ways, humans are so much worse.>>101838877
Or... White Pearl is the replacement.
Our Pearl WAS White Pearl, but was given to Pinky as a gift (old theory) which is why her gem is on her forehead and her skin is white instead of pink.
And the new White Pearl was a gift from Pink to White, with her gem originally in her belly, like Pinky's gem... but now it's in her eye, and that's how it got cracked in the first place. White didn't want her to look like that anymore after Pink died.