Considering how everyone contracts the parasite that causes the Hinamizawa Syndrome upon entering the village, yes she has been suffering it as she was conducting research there but I don't think it actually influenced her actions since what she did was all part of her goal that she had as a young child. Given what she has gone through as well as her steely determination, she isn't one to react to stress easily (somewhat similar to Mion's situation where she is trained to know well how to handle her own stress for her future as the Sonozaki leader), and for the most part things were going pretty well up until all of her years' worth of work suddenly went down the drain in a single morning all because of a group of meddling kids
I know all villagers are supposed to be infected, I was just asking myself if she reached LV 3 or whatever when she had problems with Rika's parents or even more with the Alphabet project after Koizumi's death. Maybe it was Syndrome-induced madness which made her plan the destruction of the whole village, I thought. Because Nomura was able to use her like Takano fooled people with her diaries in other arcs.
She was taking a vaccine similar to what Satoko was taking to stop the effects. I think a lot of Takano personality and how she handles things was derived from her harsh childhood. She already had some sort of complex of thinking god is out to get her. There is no vaccine for someone who view of the world is out of whack. Sometimes crazy is just crazy.