Thank you so much!! Deleting the default file worked and it seems to be running now! I'm so sorry for all the problems and I'm so glad I can continue playing the game now O^O This is a lovely game and I really appreciate the help. Strangely though I think the only thing that still seems odd is that I still cant go through the right staircase to see Yandere as I think I completed everything else. I will definitely check out the other games as well!
So, I have tried myself and it works for me. This is what I did, could you confirm this is also what you have done?
--SPOILER AHEAD---
-I downloaded the second file
-I got all common dolls
-I took scissors and matches to kill the broken dolls and Okiku-san
-I got the yandere doll and sent him away by talking to him
-I got Mirror Helen
-I chose true end
-I watched the animation and opened the dolls' room following the order on the sticker
-I went upstairs and clicked on the red book
-I chose the option "I don't have any wish"
Then I went to check the stairs next to the Japanese door and the yandere doll was there.
Just in case, I'll create a new download link with the stairs unlocked so you can play it at least :)
I think I had previously made a mistake in choosing the other option instead of "I don't have any wish" and I think that was probably why I was not able to access the staircase on the right. I followed your points by redoing the true end and it worked out!! I'm so sorry you went through the trouble of creating a new download link and I'm so glad I can experience the full gameplay now :) Thank you dev for all your support!!! This is such a pretty and fun game!