I just got back from Fallen Curst, and was finishing up the last bit of the Deionarra's Truth quest. I'm not exactly sure when she went missing, but after going through the dream with Kesai, I noticed I had an empty party slot and realized Annah was missing.

I got lazy and had been relying on quicksave, so I can't go back to before that without losing hours of progress, but I wanted to know if anyone has ever encountered this. Or, if it would be possible to get her back somehow. I checked all the places I went and couldn't find her. If not, oh well!

Playing on Windows 10, installed everything in the stickied mod guide.

I used IESE, added Annah to my party, set her as an Ally and found her in Mebbeth's hut. I guess she got left behind, and dropped from my party? Anyways, solved.