So, this story takes place in a slightly altered universe of that the show takes place in (Steven universe)

There is a fifth diamond, grey diamond.

I'm not sure if this is commonly known, but the diamonds higherarchy seems to be based on there size and gem placement.

White, being the tallest, and having her gem placed high on her forehead, has the highest order of command 

Blue and yellow, being the same height, with there gems on there chests, have the same order.

Pink being the smallest, with her gem the lowest, being placed on her stomach, is lowest in command.

Grey diamond is in between the sizes of yellow/blue and white diamond, with her gem being placed on her neck, but she's treated like she's less than pink.

In this universe, pink and grey share rule over earth.

Also, instead of a pearl, grey has a lepidolite , and is often also accompanied by a ruby.

Also, I think gems don't have to be fused into (i'll Use Garnet as an example: all Ruby's and sapphires when fused are garnets, but not all garnets are a ruby and a saphired used.) I believe this becouse of a line from blue diamond ("it calls itself a garnet?") yes she can mean hessonite and what else, but I still stick to this theory, and it will make sense why later.

 Now, at the start, you may wonder "how is this partly sanders sides?"

I tell you; "be paitient, there's a little fluff, but the start is one solid line"