Bethany (nicknamed Beth) is an unlockable character added in Antibirth.
I am going to assume you are playing this version of the game as well. Or How to Unlock Jacob and Esau in Binding of Isaac Repentance. Greed mode is all about making right item decisions and dodging. If you can't reach Chest/Dark Room consistently, you lack experience with dodging and item knowledge. In the older version, a local player could drop in as a floating baby, but all they could do was shoot and move.
