How would AT&T not charge a tax? I'm thinking you read wrong. There will be tax . Maybe it's rolled into her bill per her contract or something.
I have been checking daily since the night of preorder and nope no tax at all. I then had a 20 min convo with Apple and Att customer care and Apple explained to me that it is a state law to charge tax on the Apple website. I also just looked again and still no tax for AT&T . I was bummed but the same for all of my friends that ordered their phones no tax.