Yes, I have a point system in place for several psychological mechanisms. When they fall below a certain threshold, she starts losing touch with reality. Perhaps it could even get to the point where she becomes possessed by these beings, blurring the line between whether they're real or not, or perhaps her strong belief in them actually causes them to materialise. But of course, the game is told from the perspective of an unreliable narrator, which gives me plenty of room to play around with these concepts.

Well, the thing that makes it easier is that there are only a few highlighted words that will trigger unique dialogue, because if you write something completely unrelated to the conversation, the outcome will be entirely different. I think it would be something along the lines of the protagonist becoming increasingly confused. The text box idea also opens up the possibility of having some secret options, as well as forcing the reader to pay at least some attention. I've made the basic system for how it will work and tested it a bit. It works for now, but who knows, perhaps I'll make some changes later if it turns out to be unmanageable in the long run.