What exactly do you need to cancel?
Do you mean cancel auto-renewal so no further payments are taken from your bank card/account?
If so then just cancel it at your bank and it should be fine.
If auto-renewal wasn't enabled then you don't really need to do anything.
Unless you/she wants to retain the phone number in which case you'd need to port it to another provider.
If you need to contact 48 support about this then see the links in my signature below.
However they normally only deal with the account holder - maybe there's an exemption for minors if your daughter is not an adult.
