Luck of the Dragon by Susannah Scott

Luciana de Luca has a PhD in sass and gemology—and a problem. Her twin brother's gambling debts have gotten out of hand, and a mob enforcer is blackmailing her to rob the latest, greatest mega-casino on the Strip. Although Lucy has worked her whole life to get away from her family's grifter past, to save her brother, she dons three-inch heels and a sluts-r-us dress and struts into Alec's Gerald's casino, determined to put her long-forgotten thieving ways to the test again.

Alec Gerald, a shape-shifting dragon, has built the Crown Jewel casino to provide sanctuary for his people amongst the flash and awe of Las Vegas. Unfortunately, the sexy little thief trying to steal his largest diamond exhibit turns out to be his mate, and he must woo her before he loses his dragon form forever. But before he can handcuff her to his bed and explain the details of a mating ceremony, an enemy attacks and threatens to destroy his casino, his people, and his newfound mate.