She can put the new phone on her existing plan and phone numbers. Contract does not change, nothing chages other than the phone. If my memory serves me correctly, there is a $20 fee, billed to the account, for the hardware change.
That said, I think you'll be hard pressed to buy a phone without her being there to put it on her number right away. Handsets aren't supposed to leave the retailer without having a number in it, and if it's not your account, then she would need to be there to consent to the change.
Linear Mode
