Need much more info before we can really help. As mentioned above, what phone? Does she have a data plan?
Is the phone new, or not (was it working before, then just recently stopped working on data)?
Is the phone purchased from AT&T. If so, you should be able to go into an AT&T store, and they can get her up and running. Might be that she doesn't have a data plan, her account isn't properly provisioned, bad SIM, or incorrect APN info on the phone. All things which they can fix at the store.