I found this to be the most emotional of the 4 and there were several points where I gasped aloud - Russell being condescending and trying to push Ellie physically in their relationship, Nadine calling her fat, Magda kissing her boyfriend... it seemed a bit out of character for the girls to betray Ellie like that though after the last 3 books.
It's still so jarring to me that these girls are 13-14 and under so much pressure to be sexually active. Nadine falling prey to an online paedophile is especially shocking. After almost being pressured into sex by her 18 year old boyfriend in book 1, and disappearing off with a gang of men in book 3, you would hope she'd have learned her lesson by now but alas, it happens again. Just like it happened to my friends when we were all that age. :(