said by HiVolt:AT&T can also be lying, trying to fool her, or the agents dont know and automatically think the phone is locked because she is in a contract. If it was bought from an Apple store or Apple online it should not be locked.
IIRC, if you buy a "carrier" version iPhone unsubsidized, it will still be locked to the carrier you choose. You have to choose the "unlocked" version of the phone in order for it to be unlocked in the box. Whether or not Apple would sell you a carrier version phone unsubsidized has changed over time. It looks like they currently won't, but I do remember that unlocked iPhone 5's weren't available for a month or so after release, meaning for at least a month, every phone people bought was locked.
You can tell whether you bought a carrier version phone by whether or not it has a SIM in it when you open the box.