Just to put it straight: Hermione did not invent Protean Charm, she just did a complex bit of spell layering, making the coins warm up whenever the date was changed.
And I'll use this occasion to congratulate you on your superb writing! Alex became one of my favourite characters and I'm waiting impatiently for her fifth year.
BTW, are we ever going to see Dean Grimm lose a magical duel (not counting Ben Journey's tricks)?