Friends in High Places — Marne Davis Kellogg

Kick Keswick, once a jewel thief living an exciting double life, has now retired in simple luxury to the south of France. But when an old enemy resurfaces, threatening to expose the countless fake jewels Kick had carefully substituted during her years of secret theft, she is ready to act.
Back in London, Kick finds herself with more employment than she bargained for at a company whose status is much more precarious than she'd thought. Her enemy, in disguise, circles ever closer. And a young nun comes to Kick with a mysterious jewel-encrusted figurine, and a story of greed and murder.
To balance on this high wire, Kick must sneak into an upper-crust wedding in the Italian Alps, break into an ancient castle owned by a very modern murderer, and do it all with her customary panache, style, and grace. Can she keep one step ahead of the most seductively ruthless foe she's ever encountered?