After months of getting discouraged by the soft-locking issue, I just realized today that I could try to delete "common.rpgsave" and it worked. I was hesitant to look up anything related to that mode since I wanted to solve the puzzles myself. (The mirror room reflection was the only part I got held back on.)
And wow, I am fascinated by all the little details such as the flashbacks and the new diary entries that describe the events that occur in The Diary of Ellen book. But what I'm most fascinated about in the end is when you last speak to the cat on the bench, a ghostly figure of Ellen appears sitting next to him and the cat says "See? Looks like she feels the same."
And then when you finally escape, you can interact with the house again and a floating Ellen appears again with a happy expression, waving at you as she proceeds to ascend. After that, the house itself turns red and looks like it's melting. (This normally happens when you leave the screen and then come back)
This "ghost Ellen" acts strangely and unlike all the other times she appears around the house. Her spirit leaving the house at the end heavily implies that this figure is the spirit of the house itself. And if you've read the novel, you'll know that the house's previous Witch wished to become part of the house itself.
And since Ellen's actual soul is inside of Viola the whole time, this spirit can only be nothing but the house itself. The fact that the cat refers to the apparition as a different entity than Ellen also implies that.
If this interpretation is correct, why does she look like Ellen? Is this what her actual appearance was like or did she just take on the current witch's form? It would be pretty strange and interesting if all witches end up looking more or less the same: with purple long hair.
Interestingly, this is the first only instance where we ever get to see Ellen's actual eye color in a game. It had only ever been implied and colored that way in Fummy's other works before then.