I'm old enough to remember, albeit vaguely, that this was a much-vaunted film when it first came out, circa 1969. It was this month's pick for my online-only women-only book club; I got as far as ordering from a local library both the book and the movie but then failed to pick them up on time. I attended the meeting anyway but for some reason couldn't get heard via Zoom so participated via chat.
Then a few days later I happened to catch the final 45 minutes of the film on TCM recently. I'm now just as glad that I didn't invest any more time into this enterprise.
From the meeting discussion, I had guessed that the protagonist (or anti-heroine) was on the autism spectrum. However, now, based on what I have read online about it and from watching just the film's last section, I now repudiate that theory.
I once opined that Asperger's Syndrome (now more often called high-functioning autism) sufficiently advanced is functionally indistinguishable from sociopathy, but that description actually accurately applies to just one person I know IRL and whom I will not identify in any way. I sincerely believe that most with ASD (autism spectrum disorder, a category that probably includes me) are good people who have varying levels of trouble communicating effectively - and who are almost constitutionally incapable of lying or in any other way deliberately hurting others.
That's not Jean Brodie, in or out of her prime, though the late great Dame Maggie Smith is scary good (and won an Oscar for it) at portraying bad on the screen. This character now seems to me to be a delusional manipulative narcissist who tries almost literally to live through her students and in doing so indirectly kills a couple of them and damages at least two others. Therefore, IMHO, it is a horror film. I might change my mind were I to view the film in its entirety and/or to read the novella on which it is loosely based, but I'm not sure I can bring myself to do either.
P.S. The term Asperger's Syndrome was dropped about a decade ago, and I'm glad. It was named after a German doctor who recognized/admired those children with ASD who were high-functioning. What far too few people know is this: Asperger indeed saved those "little professors" - but damned those who were more disabled with ASD or who in any way were ill or imperfect in the view of the Third Reich, of which he was a proud member. Long before World War II, Nazis started killing (or allowing to die of exposure, starvation and so on) kids and adults, including so-called "Aryans" who failed to meet their expectations for being allowed to live.