my iphone 4s can't detect any wifi connections while other iphones & mobiles can.. pls. help!

Settings > Wi-Fi > ON

Settings > General > Reset > Reset Network Settings.

Basic troubleshooting from the User's Guide is reset, restart, restore (first from backup then as new). Try each of these steps in order until the issue is resolved.

If none of the above resolves the issue then a hardware issue exists, take the device to Apple for evaluation and possible replacement.

Warranty and support for iPhones is not and never has been International.

The only place to get warranty or support service for your device is in the US as that is where it came from.

Ship the device to y our mother in law and have her take it to an Apple store. Once the issue is fix, she can ship it back to you.

I Had this problem for a month. My phone ran out of batterie while I was out so was off for 8 hours. When I charged it next day wifi was working again.