Too bad for yuko since our monster obviously consumed her memories. I doubt her consciousness transferred to it or anything and she's simply dead and gone. The monster is just a mimic after all. I mean it was yuko who liked mc and the monster is just acting on behalf of the memory it took. I guess? It would be nice if her consciousness indeed transferred tho, then she wouldn't truly be dead.
I mean, what consciousness transference even means is a philosophical question. If every cell in your body is converted into energy for a moment and then reconstituted exactly as before, in the same location, you probably won't feel any different, but are you the same person as before or did you die? What if two exact copies are reconstituted next to each other using different atoms? Which one are you? If you say that you die in both cases, what if you're converted into energy and then reconstituted one molecule at a time per yoctosecond (it's a very small unit, and with this number it'd take about one second for the entire human body to be reconstituted)? Did you die then, even though at any moment in time you're completely whole except for that one molecule? What's the difference between being converted into energy all at once instantaneously and one molecule at a time?
The point is that it's unclear under what conditions consciousness transference would occur. Perhaps by consuming her flesh and reconstituting it as the spider's own body, that is sufficient for Yuka's consciousness to live on subjectively. At the very least, it's highly plausible that the monster now has a personality and feelings the very closely resemble those of Yuka's, i.e. for all practical purposes she IS Yuka (mixed with an alien spider). I think an argument in favor of the idea that Yuka's mind lives on is that before being eaten she had a dream from the perspective of the spider inside Rei's house, and we know that really happened, so perhaps the spider has the ability to create some kind of consciousness connection with its "victim" prior to consuming them.