Teenager has found a way of removing Norton Family Online

Teenager has removed online family from her tablet, this has been working fantastic for the past 18 months.  Noticed it wasn't registering any activity for about a month, I managed to get hold of the tablet and when I opened the App is was as though it had just been downloaded with 'GET STARTED'.  I re activiated it under a different Device name, as it would not let me use the same name and treated it as another device, once activated the old name disappeared off parental control.   This I did 23 July, it started to monitor again no problem,  Then it happened again 26th July, it stopped monitoring and checking the App it's gone again.   HOW IS THIS HAPPENING !!  It's pointless reactivating it if it can be removed by the child.