I tried to find her by the river, but I couldn't. I then tried to turn off collision and see where she was from an adjacent area, and there she was, sitting by the river, where I couldn't see her before. I turned off collision and talked to her, but I still didn't see her in the museum afterwards. Also, I replayed my previous save, and everything worked out fine, she was by the river and all. But I put more time now and I don't want to replay 5hr+ of content, and I can't just skip a big quest like this one, there's a lost fragment in the castle location in the quest as well, so it's a big deal. I really think it's a good idea to try out the npc ID for now and see what happens, it won't hurt, since it's not working right now anyway.
Note: Will test the solution provided by the mod, and edit this post with the result.
Edit: urst's solution using the console has worked.
Thank you so much for your readiness to help and your persistence.