She's on a Mac, so drivers are built in...
Friday, first plug in the external drive, next head to /Applications/Utilities and open Disk Utility. Is the external drive listed in the left hand column?
If so, click it once, then click on the First Aid pane and then click Repair Disk in the lower right hand corner. If there are any errors there, copy and paste them into the thread.
If not, check and see if a different firewire/USB2.0 cable will work. It may be that your cable is fried out.
Let me know how far you get with these instructions, and let me know.