Nothing like "spilled milk" to mention 'being more careful!' I've used "Find my iPhone several times since it became available. Only once when it was actually "lost." But it is well worth the $100 for MobileMe, just for that piece of mind.
Not sure what is "a nuisance" about WiFi, you can turn off many of the functions that use it, silence the sounds that those provide and even use vibrate should you desire. All the while still having the "Find" function enabled. But more importantly, that capability provides security functions that could mean a lot for your (and her) peace of mind. When and if you find the phone, I highly encourage you (both) to sign-up and use the "Find" service.
My best advice for actually finding the phone is to keep calling it, at least during business hours, in the hopes that some honest person will hear and answer. In performing a physical search, I always remember my youngest son's description of searching for something, "I just walk backwards in my mind!" Seemed to work for him! My problem is my mind doesn't usually go back too far!
I'm sure AT&T will be glad to cancel the phones ability to be used or disable it. The matter of the contract may be a bit more sticky to resolve, of course. And you'll still be without
that phone in meantime.
I'm just glad that I
...ever
...uhmmn, what were we talking about?