Yeah, that was too implicit if the dialogue of the queen was only a cursory read. In the latest version it is specifically mentioned by MC each time he tries to access that mirror w/o a gem.
See, that's not my issue - I knew I would need a gem to use the mirror, I just didn't know that A: crafting it was the only way to get one and B: that this was locking off actual game progress, rather than some side activity like repairing the room.