If Gracie is no longer US #2, then who is? No one. Aside from Ashley who is the clear #1, we've got 5 or so ladies who could all contend for spots 2-3, but none of whom could probably contend for a World medal this year even with clean skating aside from Gracie.
When clean:
Gracie
Mariah
Mirai (assuming no URs)
Karen
Courtney/Polina
All of these girls are question marks when it comes to consistency, either because they are known hot messes (Gracie, Courtney) or because they haven't competed enough yet this season (everyone else).
Assuming she earns it, give Ashley her National title back in January. Then let the skaters who place 2-4 grit it out against one another at 4CCs and send the two who skate the best to Worlds. Put the pressure on to skate two non-disaster competitions back to back. If whoever wins silver at Nationals bombs at 4CCs, that's too bad. Send the most reliable.
Even Gracie's bad performances last year showed that she was still good enough to play a major role in keeping those 3 spots, so she was worth sending even if she's unreliable. But fifth and eighth at GP events? Those performances would've gotten her buried at Worlds. Plus, she skated better at SA than in France, so she hasn't exactly made forward progress. She's lost the benefit of the doubt and the US can't risk sending her over someone potentially more stable. But there might not be two US ladies who can consistently outskate this year's version of Gracie.
It'd be a huge mistake to pick the Worlds team based on Nationals alone.