So I checked the artist's previous posts on Pixiv. (Twitter posts seem to be the same. Except this Danica one here.) And I don't see any indications for AI usage. Plus as commented someone, tags to posts can apparently be added by users too? So the tag is a bit of a weaker point of evidence.

However the image itself is a bit...*funky*. especially the gems on her head piece, near her throat and under her bust. Probably should be more safe than sorry in this case.