I would call it a 'cardigan coat' - a cross between a cardigan and a coat, it looks knitted rather than fabric, it's also probably not as long as it seems, as when she stands up it would be probably just above her knees.
Where to buy? At the moment I don't know, it would be available probably in autumn or spring depending on where you live and if it's 'on trend' or not, I think Zara/Mango type stores had this style in last year.