Who is Saint Clarion??
I didn’t know what you were asking about, but just remembered it was the very briefly mentioned name of the school Tenley had stole her uniform from (or maybe she just borrowed it from one of the changelings).
So the answer to your question is… no one. I made her up. I thought that Clarion was a popular fairy name and obviously there’s an elven and fairy theme throughout. Maybe she’s the patron saint of brass bands.