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

Since Mary is struggling with making a decision for herself, this would be an example of internal conflict. Characters isn't a dilemma, exposition is how the story is "set up" so that's incorrect and external conflict means she struggles with something that is NOT herself.

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