refund request, silly buyer, safe-t claim?

Pretty confused. The buyer bought the item; I shipped the item; the buyer presumably misread the item details in the shipping confirmation, thought she had ordered an unsuitable item and requested a refund whilst the item was in transit. The item is pictured and listed as having both attachments. Her reason for refund was that she had ordered attachment x but was expecting attachment y (again, both are included as standard). So, nothing wrong with the product, in fact it hadn’t even arrived, and it wouldn’t be unsuitable for the reason she gave. I messaged her, kindly explaining this, but she ignored me. It looks like she has returned the item (probably without even opening, but whatever). I am footing the bill for postage and return postage. Why? So I try to make a safe-t claim. I can’t because my account hasn’t been debited for this order??? Surely my account would be credited not debited for a customer requesting a refund? Sorry I am new to amazon and rather lost right now. TIA