Ashley still has an overall better body of work than anyone else when it comes to US Nationals + GP + International results over the past 3 seasons, including this one. She has medaled in the GP every year, finished in the top 3 at Nationals (including one US Championship), and finished in the top 7 at Worlds, including one silver World medal.
The last three seasons do not count, according to the published selection criteria. Only back to 2017 nationals counts. If they want to ignore the criteria, which I think they will, it will seem very unethical.
I actually think the US federation will send Ashley regardless of how she does in Nationals. She has secured spots for the US in the past years, and the year 2018 will most probably be her last, and it's kind of a "good bye and thank you" gift. The other two spots - I don't know. Bradie seems a good idea, as she is fresh and new, and showed she can score in Skate America. I'd personally give the third spot to Karen - she CAN be great

I never got Mirai, I think her programmes are duller than dull always and to me, she has no charisma at all.
According to the criteria, they cannot send Ashley as a goodbye gift if she screws up at nationals. I think they will send her even if it's unethical. I don't care if Mirai's programs are dull. She has been scoring generally higher than Karen this fall. IMO those two are about equal so it depends on nationals.
I'm making a consistency graph in Excel with all the tiered events, just with the current favored ladies. Tiers cannot be weighted since USFSA won't reveal their weighting metrics, so I'm doing it by earliest event to most recent. But it resembles the consistency graph that USFSA has on the last page of their selection criteria, which is not weighted.
Bradie's scores have sharply increased since World Juniors. Ashley's scores have sharply decreased since 2017 Nationals. Mirai, Karen and Mariah seem to be very close in terms of consistency but Mirai has the second highest fall international score after Bradie.
We still have Golden Spin for Bradie and Karen, and Nationals for everyone.
Here are the current scores from the selection criteria (feel free to check my accuracy.) Skaters not listed in a particular order:
Ashley:
Tier 1
TBD US Championships 2018
193.54 Worlds 2017
Tier 2
183.94 Skate Canada 2017
WD Skate America 2017
Tier 3
211.78 US Championships 2017
Karen:
Tier 1
TBD US Championships 2018
199.29 Worlds 2017
Tier 2
170.40 Skate Canada 2017
182.80 Skate America 2017
166.82 Four Continents 2017
Tier 3
TBD Golden Spin 2017
182.32 US Int'l FS Classic 2017
214.22 US Championships 2017
Mariah:
Tier 1
TBD US Championships 2018
187.23 Worlds 2017
Tier 2
188.56 Rostelecom 2017
166.04 NHK 2017
177.10 Four Continents 2017
Tier 3
168.66 US Int'l FS Classic 2017
197.92 US Championships 2017
Courtney:
Tier 1
TBD US Championships 2018
Tier 2
182.57 Skate Canada 2017
Tier 3
165.39 Warsaw Cup 2017
174.16 Autumn Classic International 2017
165.19 US Championships 2017
Bradie:
Tier 1
TBD US Championships 2018
Tier 2
204.10 Skate America 2017
Tier 3
TBD Golden Spin 2017
196.70 Lombardia 2017
161.36 World Juniors 2017
169.98 US Championships 2017
Mirai:
Tier 1
TBD US Championships 2018
Tier 2
178.25 Rostelecom 2017
194.46 NHK 2017
194.95 Four Continents 2017
Tier 3
183.54 US Int'l FS Classic 2017
194.90 US Championships 2017