I thinks it was Pink Diamond's Pearl, so should I say our Pearl

Notice the pink diamond on her suit. to shatter a diamond they had to be someone close to them, some one that they would listen to and trust. after see how Yellow and Blue Diamonds interact with their Pearls I think it's safe to say a Pearl would be close enough to qualify as the Shatterer

Mmm, doubtful. At this point, Pearl was already Rose's second in command, as the assassination occurred at a point hundreds of years into the rebellion. While Pearl most likely WAS a Pearl servant of Pink Diamond, it's hardly unreasonable to suggest Pink Diamond simply replaced her with another Pearl after the defection.