Since the new Fazbear Frights book (1:35am) came out, I've been thinking about the first story.
Could Charlie's doll Ella (from the Trilogy books) exist in the FNaF games? My answer...very possible.
What do we know about the doll in both lines of books?
The Silver Eyes, The Twisted Ones & The Fourth closet - Henry (the creator of the Freddy Fazbear Pizzeria animatronics) created Ella alongside other toys for his daughter, Charlie.
Fazbear Frights - The Ella doll was discontinued.
I'm just going to cut it short to what I think.
I believe that early on before Fazbear and all that, Henry built the Ella dolls for early income, only for them to become discontinued for some reason, probably around the Fredbear's Family Diner era.
Remember a while back, Scott gave us a hint to solve it all; Something about things seeming different to the mind of a child.
Elizabeth in Sister Location - "Didn't you make her just for me?"
Charlie in the Trilogy books - Henry had made the toys "for her"
A kid could easily mistaken a toy built by their parent as something all for them, but then it leads into something that has only just come to mind; (in the Trilogy books) Henry could have had an Ella doll laying around long after making them and just fixed it up for Charlie.
Not really a theory that changes anything I guess, felt like doing what Scott wanted us all to do; search for answers in the books to fill in some gaps to the game world and just thought of this.