Mio's sense of self worth has always been in the gutter so she's always handed out refunds for delivered products like candy. She always ate the costs and gave refunds for merch/delivery issues (on top of including free gifts in shipments), she regularly charged back donations given during streams (especially big donations); I always got the sense she felt like she didn't deserve people's money so at the first signs of trouble that instantly tipped over into giving it back to them.
These refunds might have some extra psychological baggage with them, but I think it's mostly just what she's always done. "Why would anyone ever want this now, I should give them their money back."