my daugter has lost her iphone X and find my iphone is enabaled

Apple - Find My iPhone, iPad and Mac - http://www.apple.com/icloud/find-my-iphone.html and: iCloud: Find My iPhone overview - http://support.apple.com/kb/PH2696

The following conditions ALL have to be met:

1) You have the "Find My" activated BEFORE you lose the device.

2) The device is turned on and the SIM has not been removed.

3) The device is able to connect to a registered wifi connection. (iPad, iPhone, iPod Touch) or data network (iPhone, iPad with cellular).

4) The device was not restored by a finder of the device (if it was really stolen then the thief has probably restored it unless you are running iOS7+ and activation lock is active).

iCloud: Locate your device - https://support.apple.com/kb/PH2698- "If Find My iPhone can’t locate the device, the last known location is displayed for up to 24 hours. "