What exactly is the implied meaning of the hallucinations in house beneviento?

So I've replayed village recently to freshen up for the rose dlc. One thing I distinctly remember inferring from the house beneviento stuff was that Mia somehow injected a stillborn/dead baby Rose with the megamycete and that's how she got her powers. All her voice lines in there, rose's powers, the mutated baby, the entire theme of taking mia apart to find some sort of "secret", etc. Hell, the beneviento part in shadows of rose is just a straight replay of rose's memories so clearly the house doesn't "lie".

Well on a replay I thought the exact same thing, except then I played shadows of rose. And this idea is never mentioned or explored at all, and to think of it it's not in the base game past the house either. Looking it up online it seems that I'm the only one who thought that and that Rose only gained her powers from ethan's megamycete floaters.

So, like, if I'm completely wrong, what's the point of all the beneviento parts? Why was mia so regretful? What did she do, why is she so sorry and asking ethan for forgiveness?