Can’t you just yell her keep her phone always on? If she does it systematically then it means she doesn’t want you to know where is she..

Sure she doesn’t want you to know about her location   I’m sure she is hiding something out of you.. all you need just to track phone location https://www.hoverwatch.com/track-phone-location . It will show her location real time for 24/7 and more than that you can check her social networks messages to make sure if you’re an only one in her life.