The wicked years Tome 1
Wicked. The life and times of the wicked witch of the west

Years before Dorothy and her dog crash-land, another little girl makes her presence known in Oz. This girl, Elphaba, is born with emerald-green skin-no easy burden in a land as mean and poor as Oz, where superstition and magic are not strong enough to explain or overcome the natural disasters of flood and famine. Still, Elphaba is smart, and not long after entering Shiz University, she becomes a member of a charmed circle of Oz's most promising young citizens.
But Elphaba's Oz is no utopia. The Wizard's secret police are everywhere. Animals - those creatures with voices, souls, and minds - are threatened with exile. Young Elphaba, green and wild and misunderstood, is determined to protect the Animals - even if it means combating the mysterious Wizard, even if it means risking her single chance at romance. Ever wiser in guilt and sorrow, she can find herself grateful when the world declares her a witch.
And she can even make herself glad for that young girl from Kansas.