Harriet Taylor Mill was a controversial woman in her own lifetime. Mill's own praise of her is effusive and consistent; the Autobiography is not atypical in having passages about Taylor like this:
Up to the time when I first saw her, her rich and powerful nature had chiefly unfolded itself according to the received type of feminine genius. To her outer circle she was a beauty and a wit, with an air of natural distinction, felt by all who approached her: to the inner, a woman of deep and strong feeling, of penetrating and intuitive intelligence, and of an eminently meditative and poetic nature....
In general spiritual characteristics, as well as in temperament and organisation, I have often compared her, as she was at this time, to Shelley: but in thought and intellect, Shelley, so far as his powers were developed in his short life, was but a child compared with what she ultimately became. Alike in the highest regions of speculation and in the smaller practical concerns of daily life, her mind was the same perfect instrument, piercing to the very heart and marrow of the matter; always seizing the essential idea or principle....
One could expand the list of such passages at an astonishingly great length.
Other people seem not to have been so impressed by Taylor. The Carlyles initially liked her, but Jane Carlyle eventually came to consider her an attention-seeking hypocrite and Thomas Carlyle eventually came to regard her as genuinely stupid. Of course, the Carlyles were quick to find anything they could mock someone with.
Deciding between these two depictions is complicated by the fact that the story of the relationship is surprisingly murky given how much we know about it. Harriet Taylor was born Harriet Hardy; she got the name 'Taylor' from her first marriage, to John Taylor. It was while Harriet was still married that the two met, and their behavior for the next twenty years was something of a scandal: it was never sexual, but they constantly ignored what were at the time seen to be the necessary bounds of propriety when it came to an unmarried man interacting with a married woman. Indeed, they stretched even what would be the bounds of propriety for today, since when John Taylor went out to his club each night, Mill would come by and visit Harriet. That would get people talking even today, when we are much more tolerant of adult male-female friendships outside of marriage. John Taylor eventually died from cancer in 1849 and Harriet and John Stuart were married in 1851. Despite Daniels's claim in the article that the reasons for Mill's break with the family was due solely to Harriet's harridan-ness, it seems pretty clear that the reason was that Mill's family had never been entirely thrilled at the way he and Harriet had carried on while John Taylor was alive; and Mill took their behavior as slights against Harriet. They both suffered from tuberculosis, and on a trip to the continent Harriet died at Avignon in 1858, where she was buried. Mill bought a house near the cemetery and spent most of the rest of his life there until his own death in 1873. He was buried in the same cemetery, the Cimetière de St. Véran.
Taylor does seem to have been a somewhat uncompromising woman; Mill himself says that she had "the utmost scorn of whatever was mean and cowardly, and a burning indignation at everything brutal or tyrannical, faithless or dishonourable in conduct and character". But Daniels tries to read into the whole matter a great deal for which we have no evidence whatsoever. There is no evidence at all for claims like, "Terrorized, masochistic admiration for James Mill had been replaced by terrorized masochistic admiration for Harriet Taylor," which is more like a bad novel blurb than a reasonable judgment. Mill was indeed effusive, going on and on about how much he owed her and how much he learned from her; he was in love with her, and remained in love with her all his life. Beyond that, we really don't know. One can argue that Mill was so foolishly in love with her that he never saw her accurately; but one can on the same evidence argue that he so loved her that he soon understood her better than anyone else. Either way, there is no need for the absurd histrionics of Daniels's essay.
Dale Miller's article on Harriet Taylor Mill at the SEP, by the way, is a very good introduction to the subject.