Hi my girlfriend lost her phone and we are trying to locate it

if the phone is powered off, you will not be able to locate it. May show the last location

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Niolay Said:

"How can my girlfriend locate her phone when is turn off"

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Texting the iPhone:

Text it, and ask the person who turns it on to contact you.

if she is signing into her Apple ID, she would need to use her Apple ID password, not a 'passcode'