I wasn't exactly fishing for anything specifically, but rather wanted some sort of model of how the process could work.

I grant that cognitive dissonance is a reasonable explanation for maintaining and even strengthening a position. There are plenty of contemporary examples of this ranging from politics to Covid to climate change to grammar, even.

But what is peculiar is that it would lead to consumption by a particular idea. Although this is not unheard-of (Kaczynski might be one example, and of course Hitler is always a good example of another), it is at least quite unusual. The reason is that in moving to ever-more-extreme views, one tends to provoke other sources of cognitive dissonance. For instance, if you believe firmly in women's rights, what about the cognitive dissonance of associating with people who vigorously oppose them? This tends to provide a natural limit on how far one can go.

So your explanation strikes me both as overwhelmingly plausible and largely inadequate. One would need to argue one of three things.

(1) Rowlings is in the very rare category of people who become consumed by an idea without obvious cause.

(2) Rowlings in fact is not consumed by it, and her strengthened opposition is within the normal bounds for what you get when digging in after experiencing cognitive dissonance.

(3) There is some additional factor beyond garden-variety cognitive dissonance that explains her responses.

In the case of (3), additionally, you have to argue that for some reason it is not largely due to another extremely common psychological phenomenon: the very strong coalition instinct that humans have when they feel threatened.

As tribal creatures, external threats provoke an increased expression of tribe-strengthening and tribe-seeking behaviors (demonization of opponents, blindness to flaws of those in the tribe, etc. etc.). The charge that "as a public figure, Rowlings was always under attack" fails as an explanation for this on two accounts: first, random scattered threats are not the same as a coherent organized threat (threat from "another tribe"); and second, the scale of threat--at least verbally--has changed by orders of magnitude.

Of course, multiple things can also be true at the same time. The degree of consumption could be overstated; the tribal response could be present but modest; etc. etc..

But though I think that cognitive dissonance is a fitting explanation for part of the reaction, I don't think it's sufficient. In particular, given the ubiquity and strength of tribal responses, I think one needs an argument specifically to rule that out, in the absence of an extremely strong and compelling explanation that is adequate on its own (which cognitive dissonance is not, unless coupled with an appropriate psychological disorder).