Upload & Sell: Off
I think the partial refund / credit was a mistake. You're giving up ground when there is no need to.
Have you tried explaining to her WHY there is a no refund clause? And how this effects yourself, your business, your family?
I would just end contact dead, give her an ultimatum. You don't owe her anything, she's just being harassing by the sounds of it. But now that you've given her credit, that could complicate things... you're essentially asking her to come back for a portrait session or future wedding?