Hi there,
We seem to be veering here from strict control to no control at all. I'd suggest a happy medium?
Perhaps discuss how any kind of screentime right up until sleep has been shown to have negative effects on sleep and in the long term, impacts on mental health (Google news 4 Jan on advice from doctors on no screens one hour before bed). Try to persuade that the screen should go off at a certain time, perhaps 11pm, to allow her to wind down in a healthy way. Perhaps say if she can't resist temptation to keep watching after that time, you could turn off the WiFi to help. If that doesn't work after a couple of weeks, just turn it off. If you don't know how, speak to your broadband provider.
If your DD thinks she'll have difficulty sleeping, suggest other activiites such as more traditional reading or listening to music as part of winding down. Perhaps quietly try to find out if there are any other reasons for the difficulty in sleeping? Is she on social media/are you sure it's films she's watching?
The idea that teens will self regulate after suffering the affects of a few nights of low sleep and should therefore be left to their own devices (excuse the pun) doesn't resonate with me. Screen usage is not a one-off or twice weekly late night, it's every night. There are many temptations in our lives and even adults need a helping hand to keep control. I'd say young people especially do.
I was given free reign as a sixth former and regularly stayed up with my boyfriend til 3am midweek. This clearly had an impact on my ability to focus, achieve and indeed stay awake at school - I used to fall asleep in lessons which in turn did my self esteem no good. Not blaming him for all that (!) but I think it would have been reasonable for my Dad to ask my boyf to leave by say 11.30 pm, after which I would likely have gone straight to bed, recouping about 4 hours a night.
Screens are both a blessing and a threat and should be used with purpose. I believe we should all be working now to establish habits around scheduled/managed usage to safeguard our health in whatever way suits our lifestyles best. Look at how founders/leaders of Snapchat, Apple, Microsoft and Twitter manage them, both for themselves and their children.
It's generally accepted that TVs in bedrooms are not a good idea because it's too tempting to watch into the early hours - are tablets/phones any different? I hated having a TV in my room even in my 20s, because I was too weak to turn it off and was permanently sleep-deprived!
Sustained lack of sleep in people of all ages is a serious concern and can lead to mental health issues so I'd definitely put some controls in there.
Apologies for length of post.