Thanks Cloud, Alexa and TwoGin
Hmm I really still don't know what to do 
Maybe in the next school holidays I'll put her younger siblings to bed but tell her she can decide. Atm I just say "bedtime kids" at 7:30pm
and they all say goodnight to DH and go upstairs, pack their school bags, put their clothes out for the next day, wash, brush teeth and get pyjamas on. So all 3 are in bed just after 8pm usually. I go up and read a chapter of a book aloud sitting in ds2's room but DS1 sleeps in there too atm and DD reminds me to read loudly and complains when her brother interupt because she still likes to listen usually, not always (even though she reads maze runner/ hunger games/ ready player one type stuff to herself she's enjoying listening to Kensukes Kingdom first
but I don't find that odd really as I enjoy the books I read aloud too 
)
My 11 year old usually falls asleep during the story by 8:30pm, 7 year old draw or reads a bit in bed (I do think he needs to be in bed though) and 13 year old often til 10 - I go to bed at 10 and she puts everything away and tries to sleep then if not before, I don't hear her but she claims it sometimes still takes time before she sleeps. I honestly don't know how much of that is perception - 7 year old claims he doesn't fall asleep till "nearly morning" but I've never found him awake when I go to bed.
We've tried having seperate bedtimes before mainly because we only have one bathroom upstairs, but DD usually ends up voluntarily saying she might as well go too when I send ds2... 
I think maybe I need to let DD come back down after getting ready for bed, but on the other hand she's never complained or asked...
All 3 kids have to be up at 6am. They can't get up any later as they need to be at the bus stop 100m down the road at 6:35 am - neighbor kids wait at the end of our drive at 6:30am...
Early to bed and getting up early used to work well, but for the last year or so it's clear that it's really true that childrens circadian rhythms change as they become teens!
Still not sure...