IPhoto Library has totally disappeared!

Question

I'm really hoping that someone can advise me. I switched from Windows to Mac two Christmases ago and until now would not have changed back. But now, my confidence is seriously damaged.
Here's the thing:-
The photo library on my wife's iMac has disappeared - totally.
There was no event or crash.
She simply opened iPhoto and it said "Do you want to create a library?"
I've searched with Google and done all the suggestions.
There is no iPhoto Library in 'Pictures'.
I've used iPhoto Library Manager - it will create a new library but finds no trace of the old one.
There is no 'Masters' nor "originals' folder.
Cmd-launch doesn't help.
Alt-Cmd-launch doesn't help.
There is no albumdata.xml file.
There is no library6.iphoto file.
The hard drive verified OK.
A lot of permission repaired but they usually do.
Still no sign of anything.
The Mac is a 21-inch iMac, bought Dec 2009; it's still running Snow Leopard and she has iPhoto09.
I've switched my 27-inch iMac (bought at the same time) to iPhoto11 and upgraded to Lion but my wife (like many) is seriously conservative and switching her from XP to Mac was quite enough for the time being!
I do have a backup of all but the recent photos but my confidence in Apple products is seriously damaged. I mean, I still have photos from Windows 98, 2000, and XP computers and I've never lost a single photo before (except by the usual mistakes). The notion that a Mac can simply lose every single photo without warning makes it 100% untrustworthy.
I don't use Time Machine, though I was about to start using it. But surely if I did rely on it, it would simple backup the absence of photos and they'd be lost in the backup too?
How can this have happened?
How can the photos be deleted from the hard drive without a lot of disc activity? (i.e. they must still be there?)
How can I get them back?
Any suggestions would be gratefully accepted.
Thanks.
Brian Smith, Stamford, UK.
Post Script: I have used Stellar Phoenix Photo Recovery. It insisted that I make an image onto an external drive and from that it has found 35,000 images, most of them Apple and software icons. But there are also what may be all of the photographs. It's going to take forever to go through them all and of course I can't yet say if all sets of photos have been recovered.

Answer 1

Thanks, Terrence.
I'd thought of user error, of course, but couldn't see how *everything* could have disappeared . . . . but I hadn't actually thought of accidentally moving the iPhoto Library itself to Trash. If that was done, would it have this effect - of deleting everything?
I can see how this might be the only conceivable answer but I simply don't believe it's what happened. You'd have to go into the Home folder, then pictures, and then delete the iPhoto library.
My wife definitely wouldn't have done this. I don't think she's ever used the Finder. But I occasionally use her computer so if it was done it was me wot done it! And I did recently copy some pictures across from my Mac to hers to put them on her iPad. I'm pretty sure I didn't use either iPhoto or the Finder on that occasion - but you never know.
In the absence of any other suggestions I may have to acknowledge that this may be what happened. In some ways it would be a relief. Total loss for no reason was very worrying.
Still not happy that I might have done it by accident though!
Thanks again,
Brian