Not to PL too much but I've known a few aging "psychonauts" in my time. It's hard to say, do the drugs break their brains or do people with broken brains seek out these drugs? It's often a bit of both, but hard to tell how much of each. Something tells me if she was into even mild psychedelics it was probably just experimentation - it's not exactly compatible with a high powered Oxford PhD. We'd likely have a better idea if we had testimony from anyone around her at the time. I'd put my money on wholly or mostly a broken brain combined with stress.
This is possible, but imo unlikely aside from her potentially being inspired by some of these stories. Here's an example: the actual life of John Nash. His delusions are very similar to those of most "targeted individuals" - he believed that he was being stalked by secret societies and communists, that society was full of communist infiltrators, and that he was a person of interest to them. He never had full visual hallucinations (which are extremely rare) but he did have many delusional episodes. The thing is that his belief that American society was heavily infiltrated by communists seems ridiculous to us now, but was fairly mainstream at the time, and heavily encouraged by fictional media, as well as the exposure of genuine Soviet spies in the 50s and 60s. Philip K. Dick, who was probably also schizophrenic or something similar, had his own delusions about communists, this time infiltrating the science fiction scene, going as far as sending a deranged letter to the FBI. Communists were the bogeyman, even though realistically there were very few of them, and no evidence they were organized enough in the 60s for any kind of real conspiracy.
After communists fell out of style, it became aliens, which then shifted to G-Men/men in black/black helicopters by the 80s and 90s when trust in the government cratered. Now it's stuff like gangstalking and directed energy. The directed energy stuff probably derives at least in part from the hysteria around 5G and WiFi.
I feel like Dr. Horton's delusions can easily be explained by the fact that they're a common hysteria right now, and dovetail neatly with her interest in physics. If this was the 60s, she'd probably think it was communists, just like Nash.