That was so DB! I am so incredibly proud of you, not feeding her cake! You have been calm and cool as a cucumber and you have emotion and you needed to shout this at her. What you said was all extremely reasonable. She is having a tantrum when she isn't getting what she wants, yet she is not willing to put the work in. She is being a big baby. Let her be. Just like we show our kids, certain actions have consequences.
I'm proud of ya. I have been proud of you all along, you really are good at this. But I know you had some emotion that needed to get out, some anger, and I think you did it in the best conceivable way!