godadi
I just realized that she probably doesn't use her dirty coins for the martial art technique because of the pain that comes after. It would make her vulnerable in a dangerous situation and she doesn't know how long the pain would last so she's waiting to go back to the academy where she can safely use the coins and wait for the pain to subside. Plus she won't be able to use the technique right away anyway. Just like the technique instructor Mai gave her, she'll still need to practice it. Just a thought.(~ ̄▽ ̄)~