How much to charge, or not at all? ?

I have just recently started my photography business, back in June actually. It has skyrocketed: the word has gotten out and a lot of people like my photos, so I've been doing a lot of shoots. So far, I charge $50 an hour, and then the customers can buy the photos they like from my website, which are priced pretty cheap. However, I have had numerous clients want to purchase discs with the photos on them. I don't exactly feel comfortable doing that because that gives the client the ability to take the disc to somewhere like Walmart and get the pictures printed, giving me no payment. But recently a trustworthy client has told me she just wants them to send to her mother-in-law. She said she does not mind paying a lump sum for the disc, so should I charge a great amount, or refuse to sell a disc at all?