The mystery has been solved! Huge shout-out to
OzReturner for helping me track down the specific Wizard of Oz book that appears in Sarah's bedroom. It turns out what I thought was a red flag was actually the woodsman's axe, and as
division 6 pointed out in their post the book is actually very green (and not black like I was originally thinking!). Shout-out to
Jintosh as well, who pointed out the book cover in the film was very glossy (Which it certainly is in person too).
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OzReturner also helped me track down another of Sarah's books (The Hans Anderson one), that one's still en-route to me in the mail so I'll reveal it when it gets here. As of right now I've got four of the books Sarah has in her room: The Wizard of Oz one, the Hans Anderson one, the Snow White Annual, and Outside Over There.
Of course these successes give me the urge to try and track down more of the books, though I'm not sure how likely it'll be to find some of those other books (Like the most leftmost one in the shot I posted previously, it certainly has a distinct cover but the title is completely obscured, so unless someone happens to recognize it from sight alone I don't think that one's likely to be identified.
As a fun bonus here's something I noticed from the last time I scoured through some screenshots... turns out Sarah's a Judge Dredd fan.
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