Need some help on mobile phone security

[u/Old_ManWithAComputer]

I will try to be a short as possible. My daughter, 25, lives with her husband about 7 1/2 hours from us. All of our Apple devices are basically connected through the same Apple account. There is a woman about 2 to 3 years younger than my daughter that is INFATUATED with her. The other night my wife and I were sitting watching TV and my wife's Ipad lit up. It said that the girl in question would be notified when my daughter left her apartment complex. I got upset but wife said to keep my mouth shut as she did not want my daughter to know we see some of her messages and also some of her calls. Some not all. My question is how can I go about getting the tracker off her phone, if that is possible? Can I call Verizon and see if they have the ability to block it or remove it? My daughter told her mom just this weekend that this other girl scares her because she is overly possessive and infatuated with her and just plain comes out and makes her feel very uncomfortable. Any suggestions would be appreciated. I worked in IT and IT security and retired 11 years ago so I am really not up on phone security. Thanks