So the question becomes "Can we actually lose a spot?"
I don't see any reason why we would lose a spot. Amber is usually good for a really strong SP, one that puts her in contention to medal, and then faltering in the FS. I can't see Worlds being a different scenario. Nats this year is the outlier to her usual performance pattern because she skated very well in the FS.
As far as the US chances at 3 spots... Bradie is a solid 6th, possibly 5th or even 3rd-4th under the right circumstances. I don't see anyone beating Shcherbakova this year at Worlds.
The rest of the Russian girls have each had problems this season. Trusova has had some errors (forced and unforced) with regard to her jump content and while I don't think Bradie would prevail against her under most scenarios, no one expected Tuk to beat Sasha or Kostornaia at Rostelecom a few months ago. Kostornaia's 3A is MIA and Liza has had a rough season, and I think Bradie could beat either of them based on what we've seen of the season so far.
Then there are the Japanese ladies... I'm not sure I can see Bradie getting past Kaori but Kaori has been a bit of a nervy skater in previous seasons, same with Rika, whose 3A has been hit or miss at the big competitions. My assumption is that Bradie beats one but not both, and I don't see Satoko being a factor in this conversation.
The Koreans are harder to assess but they've also been struggling to even get rink time, from what I understand, so I don't expect them to be a factor. You was dismal at NHK. Who else is there? Kurakova? An Italian girl? Paganini? One of the Finns? Honestly, if Bradie can manage to beat one of the Russians and Satoko that places her 5th. In that case, Amber would need to finish 8th... She is pretty much a headcase and I'm very concerned by that but if she can manage to duplicate her Nationals performances she can beat Satoko these days. It's not an easy path for the US to earn 3 spots but, hell, no one expected that out of our 2017 team either, and I think there is an outside chance that Bradie sneaks into 3rd if Worlds are held this spring.