it is not unreasonable to suspect that
an individual who's dishonest in one area, can also be dishonest in other areas.
That she was a good writer is possible, but her mastery of the literary craft doesn't make her writings a good source of empirical knowledge though. She had no experience in the matters or war and peace; she was just a social parasite leaching off of her rich lawyer husband while screwing around with all kinds of idle low-lifes, like Miller for example. (She refused to marry him, btw -- the lawyer money was too good to defect.)
And btw, had she been just a private individual, I wouldn't carp about any of this -- indeed this was their own business and also has no bearing on her literary aptitude -- but some here attempt to treat her as some kind of political/philosophical guru; now, that I disagree with.
She was just a horny housewife (with a literary talent perhaps -- fine, no problem here.) Her idle speculations may be curious in purely human terms, but no more than that.
And, of course, we are assuming here that she didn't play to the crowd to begin with (which, judging by her overall approach to life, is not inconceivable -- her buddy Miller had written a lot of obvious, even by his own standards, garbage, apparently just to have something to sell to his cult followers: why should Nin be any different?) Scribble what's bound to please a crowd of dunderheads and you'll never have to work for a living.