Richard, I don't know you but want to offer a bit of advice, please don't take this the wrong way.
I have been trading online for 5 years in one of the most demanding markets, PC components and systems. The DSR's are there to protect the consumer, put yourself in the customers shoes for a minute, they ordered an item off you and you no doubt gave them a delivery date, this was missed by three days, customers don't care if your cat died/you broke your leg etc. and this was the reason for the delay, she was given a specific delivery day, this was not met. She also stated that the driver appeared not to handle the item well. Unfortunatley to many online traders state that the item should be examined for damage before signing for it, she may have been caught out by this before hence why she rejected it fearing it may have been damaged. It is your duty to get the item to the customer in one piece regardless of wether they checked it or not, if it was damaged in transit the liabilty rests with you.
Can I offer you some advise based on my experience:
1: The customer is always king, if you purchased an item from a retailer who gave you bad service you would not shop there again, if you got a good service, even if this includes a refund for the wrong item sent or refund/replacement for a damaged item you would almost certainly shop there again.
2: Always get a phone number. In this case I would have contact the buyer to find out why she refused the item and then try to resolve it with her, if it was due to the item been late I would have offered to refund the postage, if she was concerned the item may have been damaged I would have asked her to to check it. She may have just had buyers remorse, if so get the item back and move on.
3: Never refund until you have the item back with you.
4: Find another courier; Interlink are ****
I hope the above does not sound like I am teaching granny to suck eggs.
Regards
Simon_M