Ais doesn't become a spirit sword anywhere in the actual story. She is listed as human because that is what she is officially listed as in story, though she is likely actually a demi-spirit of some sort. However it needs to be noted that the details and mechanism behind her existed are yet unknown and that her mother Aria is a Spirit and spirits are incapable of bearing children.

Ah I see. Do you know where the prediction comes from or why people think she will become a spirit sword at the end and stay like that? Thank you for the response by the way.

I don't think I ever seen that prediction myself, but the basis for it would be the Argonaut tale where Argo's sword is the spirit Jupiter who became a sword inorder to aid him in his quest, and Ais having some special relationship with spirits via her mother.

Ohhh ok. Yeah i didn’t know there was an Argonaut story you could actually read. So that’s where that comes from. I wonder if you actually have to be a full fledge spirit to do that or not.

There is a story like that in danmemo. Ais in wonderland or something. Ais turns into a wind spirit sword or her magic turns into that and Bell uses it to defeat the monster.