In Steven Universe: the Movie, Spinel is clueless about Pink's abandonment until the message. However, the Diamonds definitely knew about Spinel, and Pink's shattering wasn't a secret, so why didn't they tell her? Steven asks that, "You've met the Diamonds before, right?" And Spinel responds, "Yeah, but," meaning the Diamonds knew that she existed.
The Diamonds have seen Spinel before, we can see that when Pink is offered her first colony just before the drift away song. She is playing in the background and pushes into the shot at some points. Pink then abandons her in the Garden and that is the last communication she has until the message from steven. She didn't know about pink being shattered until that message.