The villain has a Player's Handbook, which as the name implies is meant for the player. It just shows the things the DM is willing to inform the player about. Names, statblocks, a bit of background info. Probably has reference tables (skills, etc) and incorporates parts of the Monster Manual.
MC stole the Dungeon Master's Guide, which has all the character and setting information, as well as the ability to edit others' character sheets. It's possible it also grants other DM-like abilities.
I imagine the evil god makes a habit of reincarnating people to play sessions by proxy with herself as the DM.