I've not seen the Store require a CC before when using a giftcard unless there is an outstanding balancing on the account? But maybe they changed the setup for account payments too? If it helps you can setup a paypal account and use that as a payment source in iTunes so that you don't have to supply your CC #. If nothing else, try going straight to the "Redeem" link in the iTunes Store and create a new account using the giftcard and see if she can make purchases that way...