I'm fairly certain Molly didn't write it at all and it was Edie later on.

The chances of a 10 year-old writing a diary as she is hallucinating, experiencing pain and being disorientated, is highly unlikely - especially with the language written. It's too creative and descriptive and doesn't match up with what Molly would have been feeling at the time.

Edie's room has a folder titled "Molly concepts". The books in Molly's and Edie's room include Norwegian folk fales, stories about cats and stories about the sea, which is what you experience in her story. When you go into Molly's room, Edith says "I got the sense Edie spent a lot of time here, before mom sealed the doors". In other words she was going in there, drawing inspiration from the stories and writing up a narrative very often - certainly well into the 2000s when Edith was alive (and poor Molly had been dead for 50-60+ years!)

On your first playthrough it would catch you off guard by making you suspect the story ties in with sinister and supernatural things. But the more you play, the more you realise the Finches were generally just a naturally unlucky/irresponsible family and Edie couldn't help but embellish how some of her children died. The Barbara story is just as bad.

I see your point. And would like to frankly disagree on your argumentation line about the writing of a 10 year old girl.

As the story plays in the 1940's and the family seemed to be kind of wealthy (I mean, they have a huge ass house) it's possible that the girl was already taught to read in an early age. (I thought it was like that, back in the days. But maybe I am totally wrong and just believe too much I see on t.v)

And if she was able to read in an early age and was entertaining herself with reading, it is pretty much possible, that she had a higher vocabulary than we are used from the kids our days.

P.S: If my english is ♥♥♥♥♥♥, I am sorry. Not my nativ language.