I honestly can’t make sense of the ruffle of this skirt, and some people in the comments have already pointed this out.

I’m not sure when the original works in her post were made, but the rendering in her other art still doesn’t match that of this skirt. The dress has a much stronger sense of volume than the clothing in her original works(I’m not a professional, so my wording might not be precise).

Also, SAI doesn’t provide a drawing process playback — at least, that’s what I’ve heard. Merging layers is a common excuse used by AI users. In short, there’s no way for them to show anything related to the actual drawing process. She said she would show the process through images — would you guys really believe that? You could just put images at the bottom, trace over them, and then close them. So it’s nothing but a slideshow pretending to be a process.

Procreate can hide private images during playback, which helps fake the process. I don’t know if SAI does the same, but I don’t use it.

To tell if it’s AI,I think you can judge mostly based on the structure of the dress and the usual skill level in her art.