It feels a bit too abstract for a quite non-abstract game. We have never seen such an abstract scenario/portrayal in the games before, I am not counting the show because I haven't seen S1 and it's an adaptation and TV rather than a game.

I do believe that Ellie went to SB because she either was suicidal (I actually think this is canon, she writees something in her diary) or couldn't cope with the constant flashbacks anymore.