How can you prevent unauthorized access to your data after iPhone theft?

Don’t do it. They can’t sell her data because they can’t get into it to see the data in the first place.

Apple's advice to remove the phone from the list is basically throwing in the towel on the phone.

Yes, the phone is gone, but you can really frustrate the bad guys who have it by not removing the phone from the list of devices using the Apple ID.

Those messages may turn into stronger threats, but just ignore them.

Do the Apple articles still talk about removing the phone from the list of devices associated with your Apple ID?

If you do that, I think that will clear Activation Lock, letting the criminals "make your daughter's phone their own."