Go to felixbruns.de, and from there download the current iOS 6 .ipsw for her phone. The files come direct from Apple's server, so there is no worry for malware. Once you have that downloaded, in iTunes ctrl-click (windows) or option-click (Mac) restore, and browse to where the location of the firmware you downloaded. From thre the rest is as usual.
If you happen to download the wrong version, it will tell you "This firmware is incompatible," so you won't have to worry about messing up the device. I hope this helps!