Bratfest at Tiffany's: Towards the end of the book Claire decides she's going to run away from the (New) Pretty Committee, Cam, and anybody else that makes her sad while she's trying to comfort and dress a baby and tell her everything's going to be better and that she can come and stay with her when she grows up and leaves her abusive mother. All of this to a baby made out of plastic.
Massie and Claire's reconciliation at the end of the next book, My Little Phony
Tale of Two Pretties, the final book: how the PC react when Massie reveals that she's broke.
And again, when Massie tells the PC that she's moving to England
Massie (to Claire): No matter how much I tried to break you of it, you're always exactly...you.
Heartwarming combined with Tear Jerker: Massie working hard throughout the entirety of Tale of Two Pretties to get what she wants like she always does - but this time, she actually does it through honest, hard work (telling the rest of the PC the truth, organizing a sale of used clothes to raise money) with the end goal being to stay with Claire for the rest of the semester. And then when it looks like she's not going to get what she wants, her parents finally acquiesce - only for Massie to deliberately turn it down, finally realizing that not getting what she wants all the time can lead to better things.
Massie and Layne's animosity slowly growing into a Friendly Enemy-type of rivalry as they ended up having to rely on each other in various ventures, culminating in Layne unofficially being inducted into the PC at the very end of the series and Massie adding Layne's bracelet to the four others.