I just read Cathy Horyn's review of this in the NYTimes, and not quite certain I agree with her sentiment.
Chomping at the bit (as the US publication is so late coming), I ordered it form Amazon UK and read it in a day and a half. I will have to re-read again, as there was so much good there, and interesting bits about this strange, truly eccentric, magical creature.
I devour all news of Issy because she truly was eccentric, and committed; and Auntie Mame-like, and focused, and dead-on, and I don't mean that to be a bad pun.
CH seems to think her husband, Detmar, more annoyed by her not being included in any of the deals that happened to those she discovered and helped.
Yet, I suppose that I sympathize more with her....
 I am a creative person, and know all too well how difficult it is to market and place a value, charge an amount, for "intellectual and creative property" I have, therefore, had my brain picked dry, ideas outright stolen, and watched others, on occasion, make money on my ideas, knowledge, "eye"... 
Because it is not a solid commodity, others easily dismiss it, all the while thriving on it.
I've also dealt with bouts of the blues, and know how excrutiaing that can be. As bad as mine have ever been, I've never been driven to the end that she was, and I can only imagine how desperate she felt to escape her pain.
Hats off, or, perhaps, more fittingly, HATS ON... to Issy!!!!!