The only problem with your "if" scenario is that we have some pretty solid evidence of how well Sarah, Elyce, Alysa will score when they DO stay upright through their FS at a GP. Alysa didn't pop any of her jumps at SCI - we know what the tech panel did to her TES. Same with Elyce at SCI - we know what the tech panel did.
I know a lot of us have our personal opinions on where Sarah's PCS should be but it seems pretty clear, through 3 different Challengers and GPs that international panels do NOT agree with your assessments. Could a different panel see things differently and suddenly drop her PCS to the level you think she should be at? Sure. Is that likely? Not as long as she stays upright, IMO.
Her scores are CRAZY consistent - and it's not as if she's had a home field advantage at any of these events except Cranberry. She has no built-in advantage of competing at a home GP (Isabeau, Bradie, Elyce), she has no advantage of being a World Medalist (Isabeau, Alysa), she has no advantage of being a former US champ (Amber, Isabeau, Bradie, Alysa). And yet, her we are, halfway through the GP, with Sarah having the 2nd highest score of all the US women (with Lindsay still to debut). We'll see where things stand in another three weeks, but if things remain the same, then I'm betting that if she's in the Top 3 at Nats, she's getting named to the Worlds team whether any of you like it or her lack of personality on the ice or not.