After its all set up, test by moving all her photos to another location on her machine, wait until she notices they are missing, then calmly proceed to recover them from the NAS.
If you survive, it will then be clear to her how important it is ;)
And as others have said - HDD's can fail. I prefer to view it as they WILL fail, so what happens when they do is the important thing to consider.
Also, you mentioned about wireless access (backups??). Be aware that if you start pumping large backups across your wireless, not only is it likely slower compared to direct connection, its also going to choke the wireless for other users.
Steve

