The dilemma that mary faces when she must decide whether or not to become a heroine, like the ones that she reads about at school, can best be described as

characters

external conflict

exposition

internal conflict

Shes not telling anyone what her problem is so exposition is out, she isn't facing a conflict with anything or anyone so external conflict is out, and (What I'm going think is characterization) she isn't gaining any depth or showing a new detail about herself so characterization is out, so that means internal conflict must be the right answer, hope this helps