This is a good time to sit down with her and have a talk over. Explain that this situation has been reevaluated and will, from now on be different. That’s really not her phone because you provided it, pay for the plan etc. computer, phone all internet access goes through you. The agreement is you get to check on what she is doing/viewing at any time. Any attempt to hide the screen when you ask to see what she is doing is grounds for loss of privileges. Start with a day and double with each infraction. No switching screens, no tipping the screen down so you can’t see, you have complete access to history as well, no wiping histories. She is a child and you are her parent. Privacy is a privilege as far as devices are concerned and will be earned with actions and as she becomes older. Be ready for tears and tantrums. Stand firm. Also there are plenty of apps to help block her access to certain sites, use them!! If she removes them, loss of privileges again. You can also cut what access she has on your phone. There should be the rule of hours of operation. Not before 8am or after 6pm or whatever time you choose. Or only 2 or 3 hrs a day activity. Your call but I would suggest starting out with only a little bit of time. This is for her safety and to teach her safe practices online.