I adored Natasha's previous novel, A Kiss from Mr Fitzgerald, and I think Her Mother's Secret is even better. Although both novels are set in New York in the 1920s, they are independent stories of independent women with no crossover (though I think you should read them both).
I found this story emotionally engaging from the beginning. I was intrigued to see how the romance would be resolved, at one point I couldn't see any way for it to work out. I loved Leo's strong character and her drive to achieve against all odds. The novel was well researched and the portrayal of day to day life in the 1920s was authentic and fascinating. And the plot twists... Kept me turning the pages.
The perfect red lipstick may be a different shade for different women, but this is a book that would suit everyone.