how did calliope have a dream self if she never officially entered the game?

She needed to have one so that Caliborn could kill her and predominate early.

If she didn’t have a dreamself then Caliborn wouldn’t have been able to do that, then Callie would be able to play the game but in order to play the game you need a dreamself so she’d have a dreamself for Caliborn to kill, etc etc

Basically, Plot Reasons