I bought some melatonin from Piping Rock - this has turned out to be a godsend to me, my 17 year old and my 13 year old. All of us have struggled with sleep issues - but taking this for a few nights has been a massive help.
I don't know if you can get it prescribed in the UK without going through years of waiting to see a consultant and getting diagnosed with ADHD or similar though. I don't really understand why I can go online and buy it easily from many other countries around the world, but you can't even get a GP to prescribe it here, even for just a few days to try to get sleep back on track.
Do you or her dad have a work employee assistance program? These usually support your family as well and it could benefit your daughter to speak to a counsellor in case it is anxiety keeping her from falling asleep?
Could she be going to bed too early? That can impact your ability to fall asleep. My 13 (literally only just turned 13 a week ago) year old goes to bed between 9 and 9.30pm, is allowed 30 mins of reading etc to wind down and it's sleep time by 10.30pm latest. This definitely helped him a little before I got the melatonin (and he doesn't take it every night).
She doesn't need to be waking you if she can't sleep at her age. Tell her she can grab herself a drink or a snack if hunger is keeping her awake. Tell her to read a book if she can't sleep. Tell her to go downstairs and do quiet housework if she can't sleep (I bet she can stay in bed then!) etc. Ask her what will waking you up do to help? Absolutely nothing.
Check she is doing enough exercise in the day to physically exert herself to be tired enough to sleep.
Good luck! Insomnia sucks