Let's think it from the other way. What IF what you said was true? That the "perfect world" was indeed the real world, and because Rika was unhappy with the real world, this triggered her L5 syndrome (or just phycological sickness), so she created hanyuu to be her dearest family/friend and in the end, under the words of hanyuu, she killed her mother? Afterwards she tries to escape the reality by creating alternative worlds in her mind. This will be an intersting interpretation, although not much supporting facts for it.
But it's interesting to note that in that "perfect" world, nobody has their "original percieved sin" in game.
K1 never assult the girl
Mion never switch place with her sister and taken her position
Rena didn't perceived that she's the reason her parents divorced
Satoko never pushed down and killed her parents
Takano is a happy girl that is not even in the chapter (This world is actually a part of the hidden piece #52? Maybe....)
In the end it was the "sinless" Rika that committed Sin in this chapter. (And I can always argue Rika was having mental instability like K1 did in the first chapter)
She herself destroyed that world and made that world imperfect, just to be back to the old world....
Like the story says, if Rika choose to stay in the "perfect world", then the previous worlds are just a dream. If she choose the old world, then the "perfect world" is just a dream.
What world would you have choosen? For me I would have choosen the perfect world. I think the major reason would be i can't bring myself to commit that "sin"...
Well even if all the worlds are not Rika's imagination, all these are just 07-san's creative imagination lol.
Anyway Higurashi is an entertaining series, and glad this chapter maintain that entertainment