In MD, Betty/Diane is a reincarnation. She was brought to Hollywood for a second chance at life because in her previous life she discovered that she had a talent for acting (in the 'street' sense). Hence a desire to 'act' was born, symbolized by the conception of Betty that we see in the opening scene. In her previous life this girl was a victim of sexual abuse, which contributed to her troubled life. In Hollywood, her story repeats.
Arriving at the dinner party, Diane is led up the hill like a child. Camilla and Adam represent her parents. Throughout the entire second part of MD (not just the dinner party), Camilla takes on the role of the father. Rita/Camilla takes advantage of Betty's sexual innocence and breaks her down emotionally, the same way that a parent whom you rely on for love and support is also sexually abusive. The on/off attitude of Camilla towards Diane depicts this process and creates hurt and confusion in Diane like it did to the sexually abused teen.
Adam represents the mother, who hardly noticed the girl's existence. Wilkins is the bother who once walked in on dad in bed with the daughter and was told it is better to forget he ever saw it. CoCo plays the grandmother who the girl once told about what her father did, but she didn't belive her or chose to ignore it. Notice the reaction of Wilkins when CoCo says "I see" and pats Diane on the hand. They know, but turn the other cheek. Dad was a respectible person in the community and any leak of such rumors would tarnish his reputation and have bad consequences for the family. Luigi plays a family friend (Dad's best friend) who shoots a knowing glance at the girl and later confronts her after the party to try to blackmail her for sex. He knows that she has been working nights at the brothel in town.
Through the perspective of the character that this girl reincarnated into (Diane), we see how terrible her upbringing was in her former life. Rita/Camilla's sexually manipulating and emotionally abusive attitude towards Diane and the lack of support that she received from others at the party replays this girl's family upbringing (in a Hollywood setting) and the end result of her story is very much the same.


