I'm sure the giver of this RAK would appreciate anything you would send her, card or gift, but she is probably not expecting anything in return.
When I was big into RAK lists, I often put in my note that the receiver could show their appreciation by sending a RAK to someone else. You know the old adage.."better to give than to receive."
Isn't it a great feeling to receive such a wonderful surprise in the mail??!
HTH
Ashley