So, in the Trial, Blue Zircon defended Steven strongly. I think she was right in saying that a Diamond shattered Pink. After all, in real life the only thing that can really break a diamond is another diamond.
You see, Blue Zircon accused the diamonds of shattering Pink Diamond. Which would make sense. One of them could say that they were going to visit Pink and then take a weapon... BOOOM! Shattered.
So Yellow now has control over Earth (kinda). I think that she knew that she was next in line for Earth, so she went up and shattered Pink to get it. And I mean, that is so evil because Pink is like her little sister, but it makes sense for Yellow because she is freaking ruthless. That also explains why Yellow wants to get rid of the Zoo. She wants to get rid of anything having to do with Pink so she can never be discovered.
And also, I mean we know how Rose was. She bubbled Bismuth because she had made a weapon that could destroy gems! She would never do it herself. Sure she would like defeat and bubble gems, but she would never truly hurt anybody.
Plus, okay, everyone is like "Well Eyeball saw it with her own eyes!" She only has one eye! And come on. The Rubies are not very smart guys! Doc counted an extra Ruby because she didn't count herself. It is ridiculous to think that a Ruby is a good eyewitness!
So, Yellow shattered Pink because she is ruthless lady who was bound and determined to take Earth for herself. Poor Pink, honestly, being killed by her own sister.