I can tell you that I can find Roxy in the encounters menu on my save file.
I did want to check your file but as soon as I hit the 'Stats' button on your codex it gives me the error:
findRoomByName(...) is null
so I can't actually check it.
But, I think this crash is because you're on the backer's build and I only have access to the public build. (I think, you do have the ‘Dance Heaven’ System in the inventory so that's why I'm assuming.)
So possibly this Roxy bug is backer's version exclusive?