The Title "Scattered Piece" comes from the Season 1 song "It's Gonna Be A Long Night" and refers to The Different Time lines merging as we encounter more hospital scenes from the original series.
As we enter the first part of the season finale the pressure on Doris really intensified. Even some of the events she witnessed from the past like Bruno's father dying and Holly's anorexia add to that pressure and the enormous guilt she feels about not being able to help her friends, either now or at the time the events actually happened. The reader doesn't know it and in fact at the time of writing I didn't know it but this guilt she feels is partly why she's in the past. She has issues to work through so that she can heal herself from the wounds and scars of the past.
Mrs Berg is very harsh and almost cruel here. She does know what is happening to Doris and really is trying to help her although perhaps it doesn't seem like that in this episode.
Doris expresses some of the questions and thoughts the reader may be having, like how does Mrs Berg know these things and how complicated things seem to be getting. However there are no real answers as to be honest I didn't quite have them myself at the time of writing. I knew where this season was ending and the ending of Season 3 but that was it at that point.
For me the main issues I had to get over here was how someone like Doris could even consider taking someone else's life. We she her struggling with the issues and repeatedly saying she can't do it and it's not in her personality but deep down she knows she has no choice. So slowly starts to think of ways she can go through with it.
The we have the flash of memory where Doris sees the pillow and struggles to breath for a moment. Which gives her the inspiration to decide to suffocate Nicole. Doris doesn't realise it at this point but there is a reason why she had this vision.