The Girl in the Steel Corset (Steampunk Chronicles #1) by Kady Cross

In 1897 England, sixteen-year-old Finley Jayne has no one…except the "thing" inside her.
When a young lord tries to take advantage of Finley, she fights back. And wins. But no normal Victorian girl has a darker side that makes her capable of knocking out a full-grown man with one punch….
Only Griffin King sees the magical darkness inside her that says she's special, says she's one of them. The orphaned duke takes her in from the gaslit streets against the wishes of his band of misfits: Emily, who has her own special abilities and an unrequited love for Sam, who is part robot; and Jasper, an American cowboy with a shadowy secret.
Griffin's investigating a criminal called The Machinist, the mastermind behind several recent crimes by automatons. Finley thinks she can help—and finally be a part of something, finally fit in.
But The Machinist wants to tear Griff's little company of strays apart, and it isn't long before trust is tested on all sides. At least Finley knows whose side she's on—even if it seems no one believes her.