Wolves in Chic Clothing, by Jill Kargman

Fun fluffy bitchy New York socialites Pygmalion thing. Julia Pearce is working in an exclusive jewelly shop, when she is noticed by the heiress for the company, Lell. Lell decides to make Julia the new It girl around town, but Julia's social successes cause trouble between them, especially when Lell's new husband gets into Julia. Bath book- I wouldn't recommend it, but it was a great bubble bath book.
Actually, I really think I've read something else by these two. Going to look that up now.