A Slipper in the Smoke by Katherine MacDonald

All Elena wants to do is escape her tyrannical stepmother and return to her beloved Navarra. Meeting a handsome stranger from the palace offers her a chance at happiness, but everything is thrown into jeopardy when she runs into a rebel by the name of Snowdrop.
Elena finds herself embroiled in an assassination attempt against a hapless prince. If she doesn’t assist the Rebellion, the Mechanical Kingdoms could be plunged into a civil war.
And yet, if the Rebellion is to succeed, Elena will have to sacrifice everything she’s worked so hard to accomplish… and the man who has claimed her heart.