I know. It's not straightforward. That's why parenting a teenager is so difficult - it's a time when things shift and change, and things that worked before stop working, and new situations arise and you have no idea how to deal with them!
And you have to start giving them more control over their own lives, or they will fight you for it, and you will almost certainly lose. 
Of course she'll need down-time. If you are convinced she is currently asleep by 10pm, then yes, she'll need to hand over her tech at 9:30pm. But if, realistically, you know she's not asleep til 10:30-11 most nights (which is the case with my DS, whatever time he goes up to bed), then a 10pm hand-over is fine IMO.
It's hard to find reliable info. I found this Irish academic study which seems comprehensive and reliable.
It reports that 90% of 9-16 year olds use social media, incl. 75% of 13-14yos - and more girls than boys. 56% of 13-14yos are allowed to go online any time, without parental supervision.
Of course she won't be a 'social pariah', but she'll be in a minority, and she won't like it. No doubt she'll survive, but she'll fight you, and you will have added stress. The question is, is it worth it? If it is, fine, then you'll just have to have the battle. But if not, then 'don't sweat the small stuff', as they say.
The US National Sleep Foundation has done some research into teenagers' sleep needs. It says they need +8.5hrs per night at least, but only 15% of them get it on a school night.
It is a well established fact that teenagers' body clocks change, and that their natural 'bedtime' (the time melatonin makes us feel sleepy) is later than both younger children's and adults - around 11pm-1am (see NSF website above, and this BBC science article ).
The problem with teenagers' sleep is widespread, and it's to do with their getting up times, not their bedtimes. I've never understood why school starts at 9am and not midday for teenagers - which would make much more sense! Meanwhile while we plan the revolution 
if your DD, like many teens, isn't ready to sleep at 9 or 10pm, then it seems to me there's little point in trying to force her - because you're actually fighting against her body clock and hormones, so you're likely to lose! She can do what most teens do, and sleep all weekend to catch up - and you'll have a much more stress-free family life!