It was her idea to steal it, initially mentioning it to Marcus as he walked to the DR. It was then her idea to actually go and steal it; which she proceeded to do. Charlie, for some bizarre reason, just suggested to take the blame. She then drank the Cider, along with Charlie.
So it's all her doing, I have no idea why some FMs were including Charlie in this, it was Sophie. Yes he had some of the drink too, but the idea, theft and motivation behind it was all Sophie's doing.
Notice how clever Marcus was - "I bet Sophie's stealing my cider now as we speak". Wow!
Very clever guy.