Set up parent with iTunes account on my credit card - HOW?

I've just set my Mum up with an iTunes account. I used my credit card details as I'm happy to pay for her but all her own address and email details. Now iTunes keeps emailing her saying someone is accessing her account etc. We are not confused but iTunes seems to be. Is there a simple way round this? I don't want the free option as I want her to buy stuff and enjoy it and don't mind paying. Any suggestions?