Hello my friend, I am having difficulty solving this puzzle. I have walked all over Stella's space and I have not been able to find Rosette's doll. Is there a problem with the game? 
Viewing post in Thou, Eternal Everbloom (18+) comments
I don't know how to explain it, but I'll try. When you enter the sewers, go straight ahead. Don't go into the vertical crack; continue a little further on. You'll find something like a giant tunnel. Go into the middle of it, and it will take you in another direction. Keep walking, and you'll see a large crack in the wall. Tap on your character and choose one of the abilities that will transport you to another location, where you'll find a stone door.