It should be fine for her to pay you for the costs of reproducing the calendars. It's only if you were making money from the designs that there might be copyright issues. But you could also tell her that it's a "one of a kind, limited edition."
On the other hand, you should also feel very flattered by her reaction. MNy hand-created gifts are snubbed by the reciever. Congrats on making such a big impression on your family!