It's Magic Dust

Magic Dust. That's what she tells her sisters their dad sells. Magic Dust that makes people happy. It makes them happy when they shout at you for taking it. It makes them happy when they're crying for shouting at you. Sinead knows no one who uses Magic Dust is ever REALLY happy; her dad's proof enough of that. Not that she's complaining; Sinead Corbett NEVER complains. Not when her mum throws bottles at her head. Not when her dad screams at her for stealing from his Magic Dust supply. And ESPECIALLY not when she's the one taking her sister to A&E when she has another 'fall'.
But somewhere between the less than charming Abner Delihare stalking her and her twin sister for the Magic Dust their dad sells, and the pressure of having to keep her family together, Sinead starts to think that sometimes all you need is a good bitching session to keep yourself together.