I suspect there are at least a couple of reasons unrelated to her music (which I admittedly don't know much about myself) why she gets particularly disliked - the fact that Lennon had been part of one of the, if not the, greatest bands of all time, and her influence is blamed for Lennon going off in the musical directions he did, plus I imagine a bit of racism (conscious or unconscious) also comes into play for some people, especially decades ago when she was most relevant.