I think Diane's limo ride and the events afterward pretty much sum up what this movie is about.
Diane is on a long and winding road to becoming a star. But it's more important for her to be known as a great actress. She hopes to be both.
This trip is interrupted by Camilla. Camilla wants to show her a shortcut. This is what the trip up the path, and everything we see at the party, represents.
When they reach the top, Adam presents the both of them a glass of wine. He declares his love for Camilla. Diane does the same. Camilla remains silent. This silence speaks volumes. She is using them both. She uses everyone. As a 'shortcut'. She also loves to have others take on any guilt she should feel. "Sorry I was late." Once inside, someone brought up Camilla's relationship with Luigi, a powerful man in Hollywood. Camilla denies it. She receives a kiss from a star. She's using her, too. She helps Camilla get some parts in some of her films.
All of the events before the party are supposed to show Diane a fast-track to the top. The party itself reveals the fruit of Camilla's labor. But it's not what Diane wants for herself. She knows that stars can fall.
Diane has a dream where she teaches Camilla that being known as a great actress is much more fulfilling. And that stomping on people, on the way to the top, will leave no one to 'cry over you' when you're gone.

