The one thing I would say is please don't blame yourself. Kids of 14/15/16 are not little kids any more and have to take responsibility for their own learning. They are, coincidentally, at a stage in their lives and development where the brain is not particularly well suited to being self motivated and self driven.
I know my daughter isn't perfect, but supply teachers have had an impact and so has the total over-selling of expectations and the under-delivery of analysis after exams taken so far. Surely, if tests get taken the results should form part of an action plan. Apparently, that's not how it works.
That's the part that annoys me. Sorry...I'm ranting again.
The key thing to take though is that as parents, you can't hang over your kids. I know mine would hate it if I hung over her and sorted out a timetable for her revision or anything similar. Having said that we have asked her to tell us exactly what homework she has every night so we can at least track the work coming in. We can't really track it going back as she's 16 in 10 days. She'll be old enough to get married in Gretna if she so chooses.
We are talking about near adults. Your dd has the same opportunity as mine to focus on her exams from now. I've told dd to concentrate on Maths and English, with science as a third priority. Anything else she gets is a bonus. You've trusted your child and that will pay off dividends in terms of her independence. She seems to know she hasn't done as much as she can and that might shock her into action.
I hope she pulls it out of the bag. I hope mine does too!! But if she doesn't for any reason, there are options she can take and I am starting to look into what those might be. We plan, they follow or they don't...then we have a back up plan, just in case.