One reason I felt I had to handle it this way despite how peeved I am about it is because I didn't have any policies posted in my shop. That has been corrected so that I won't feel obligated to do this again for the next idiot. It now clearly states that I am not fond of returns but will work with my customers to keep them happy if there is an actual issue. It also states that any shipping for returns will be on the buyer and advises my buyers to pay attention to item descriptions as they include measurements for all my products and that I am not responsible for items damaged by the buyer after I've shipped!
I think what really gets my goat about this lady is that the tone of her email insinuates that it's my fault she cut her sling because of the packaging. I should thank her for setting me straight about making sure my policies are well defined.