To reinstall Dial Up Networking (which also reinstalls TCP/IP):
Go into Control Panelm then Add/Remove Programs, to the Windows Setup tab
Uncheck "Dial Up Networking" then click OK all the way out.
Don't reboot when it asks you to (don't need to for this).
Go back into Add/Remove Programs, Windows Setup tab
Put the check back into "Dial Up Networking", click OK all the way out and reboot.
Your DUN and TCP/IP has now been reinstalled.
I work at an ISP and used to do dialup support. The above procedure would fix "no dataflow" problems about 90% of the time.
Also (and this will seem strange) have her make sure her phone cord is going into the LINE jack in the modem, not the PHONE jack. (I've seen the connection work fine for a couple years in the wrong jack, then stop working).
If that doesn't do it, go into My Computer, Dial Up Networking and the properties of the dialup connection. Write down the phone number and any other settings in there.
Delete that dialup connection and make a new one with the "Make New Connection" icon, put the settings into the new one. (Those connections can get corrupted from time to time).
Hope that helps!
And now I have to go to therapy from the flashbacks of supporting dialup customers
