If she had taken her money to the game and only returned with $15 out of $100, you would not have noticed. And I'd guess you figure what she "wastes" her money on is her business... and she likely has the same attitude towards your spending.
It doesn't sound like she is in a position where she would have to "snitch" small change from you for what she wants to blow it on.
And you are right about trust, TAB, so I think you are just curious about what she might find worth $60 on a trip to a neighborhood football game