(How much of that is owed to her being in love with him, how much to her identifying with him - as a genius unappreciated by lesser beings and destroyed by the hostile circumstances of a world not ready for him/her - both of which she was at least partly aware of doing, may never be known.)

"Les Misérables" is a good example of this (though a bad one in other points; Hugo includes quite a few 'pages of history' for which, in providing them as a contextualisation of his action, he implicitly claims accuracy, even though in writing a novel he is not sworn to any such thing): Hugo could have called his Enjolras Charles Jeanne and placed his barricade at Saint-Merri, but he doesn't, he takes a very real insurrection and in its context realistically sets up a fictional barricade, where the personal tragedies of his characters can play out against a background of greater affairs, with a fictional leader, whom he can depict as as many ideals incarnate as he likes - imagine he had given the whole radiantly beautiful charming/terrible angelically chaste firy/icy marble Spartan treatment to Jeanne! (Perhaps most notable in this context is that he doesn't give it to Saint-Just in his "93".) In my eyes, that would have done damage to the historical personnage, and unnecessarily so, since the adventures can be told, the same great points made through fictional characters. And that in turn applies a thousand times to fiction that doesn't want to make Great Points in the first place.
It's different again (as Sibylla said) in cases where the author makes it absolutely clear that they are primarily playing around - for instance, I would not even be tempted to take Naomi Novik's word on the Napoleonic Wars and thereby come to believe that Admiral Nelson survived Trafalgar, because it's clear that she's playing merry hell with history (and aware of it) from the fact that There Are Dragons! I could (in keeping with what I said above - I've probably contradicted myself five times over by now ;D) demand that she stay away from all real persons, but I do think it's different, since she actually creates a whole 'nother history that every reader can easily distinguish from the real one, as opposed to taking said real one and making changes so small/realistic there remains a temptation to believe it - or believe the author believes it.

There is a 'biographical study with selected letters' of S. P. in English that I have read by Daniel Gerould, who also edited the translation of the two plays, and Jadwiga Kosicka (the biography is short, but understandably so, but I wish there were more letters); going by that, she was a morphine addict from circa 1921 onwards until the end of her life, so all she produced while understanding herself as 'exclusively a writer' would have been created under the influence of the drug. Taking the longevity of her habit into account, I wouldn't 'blame' it for any oddities in her writing (that is to say, not to the extent of claiming that she would have turned out something altogether less idiosyncratic without it), nor for her mental state - the three forces (morphine addiction and destitution, mental imbalance, writing) all seem to have enabled one another.
I've not read any of her father's writings (another thing I always mean to do) so I can't compare them in style, but he seems to have been one of the most decisive influences in her life, artistically and otherwise; she spent some of her later years trying to 'improve' the flaws in his writing. As for leaving Freud out of it, her second Revolution-related play (after the first completed draft of "Thermidor"), "93", apparently (as I understand it, nothing has survived of this even in Polish?) centered around a young aristocrat who denounces her father in order to see his reaction ... yeah.