I'm now reading Sonia Purnell's Kingmaker: Pamela Harriman's Astonishing Life of Power, Seduction, and Intrigue, and it is absolutely fascinating. I appreciate the tone that the Purnell has taken -- instead of focusing on the salacious bits (of which there are plenty), she focuses on Harriman's intellect, instinct, and sense of strategy, which were set alight when she married into the Churchill family at 19 and was flung into a world of heavy political hitters from home and abroad.
I first encountered Pamela Harriman in the book The Daughters of Yalta: The Churchills, Roosevelts, and Harrimans -- a Story of Love and War by Catherine Grace Katz. Pamela Harriman was a supporting character in this story, but she was so intriguing I jumped on the chance to read more when Kingmaker came out. (By the way The Daughters of Yalta is also very interesting -- it's about how three young women basically kept the men upright and made sure they could find the bathroom all through the Yalta Conference.)
Totally expectedly, the first Goodreads review of Kingmaker is by a man offended that the book gives Harriman a lot of credit for the successful results of the political causes she supported.
I've also read by the same author Clementine: The Life of Mrs. Winston Churchill, which I liked, and A Woman of No Importance: The Untold Story of the American Spy Who Helped Win WWII, which I DNF due to the heaps of hyperbole.