Sure, adding the fee is a good idea. Be it business, or just plain common sense. PayPal is out to make money of of your transaction of course.
Your purchaser chose to make a PayPal payment in lieu of the other options for
her convenience. This is not a
"cost of doing business" 
If anyone works their company like this for a very long time, it will soon
cost them their business As breeders, we spend so much of the profit on these puppys, before they go. That comes with breeding, it's expected. If someone wants to use paypal, they can pay the fee. JMHO