iPhone iOS6.0.1 / iP4 / Can't switch WIFI on!

HELP!

My sister has an iPhone 4 that has been great for over 2 years now. She updated to iOS6 when it was released with no problems at all. She then updated to 6.0.1 and now can not turn wifi on. That is, the wifi toggle switch does not respond, it is always 'off'.

We have tried (well, I have suggested, she has tried!) the following:

reset network settings - nope
reset all settings - nope
erase all content and reset all settings - nope
restore and set up from backup (itunes) - nope
restore and set up as new device - nope

At this point I am stuck. What could have caused this? (I suspect 6.0.1!) and how can she fix it? I have suggested she waits a few weeks hoping for 6.0.2 update and maybe that will fix it but if that is a long way from release or doesn't fix it, or maybe there is something she can do to fix it then that would be better.

Can anyone help please?

Thanks for the replies.

Have tried a clean restore and clean install in iTunes and it still doesnt work. Could it be the ios file that my sis has saved is itself the fault? If she deleted the file and hit restore would it force iTunes to download a fresh copy from apple and reinstall that?

Update

Sis deleted the ipsw file and did a clean restore as a new phone. Nothing. Still no wifi. She is going up see apple and expects to face the out of warranty replacement cost.

Thanks guys.

Yeah she has tried the hard reboot route too. I'm guessing she has dropped it or spilled liquid on it or something and its somehow only affected the wifi. Anyhow she is visiting me next weekend and our local apple store is only a few miles from here so I'm sure she will get it sorted then.