If you disable data altogether (wifi, not just mobile), you don't really need any screentime limits or other rules such as where she is allowed to use it. She'll very quickly self-limit the amount of time she spends on it. Keeping in touch works fine with voice and sms.
As we all know., the internet is an infinite time sink.
it depends on personality. i spend more time on the internet if access is limited because i want to make the most of it, whereas if i have unlimited access it is much easier to take a break, because i can get back any time.
self-discipline is easier to learn if i am in control, not when it is forced on me. the key is to find other more interesting things to do
As we all know., the internet is an infinite time sink.