Regardless of age, I think all kids need someone to say "Don't worry - everything is going to be fine".
Firstly I've come to think that displaying "hope" is incredibly important - especially at those times when you have to admit you don't quite know what the next move will be - hope is a way of displaying an inner confidence that you will find ways, that you will find opportunities, that you will overcome problems.
Secondly - I think it so important to help your kids understand that life is full of uncertainty - some of the most important things that happen in life you have no control over - someone falls ill or dies, your company makes you redundant, people you love and trust let you down - they can be difficult times but you have to learn to accept that these things inevitably do happen and you need to learn to roll with the punches - uncertainty needs embracing - you have to learn to face up to it and not to fear it - often these setback provide opportunities to get closer or to move in the direction towards what you really want in life - I think some people might think this way of looking at things runs counter to the idea of protecting your kids from upset and wanting to provide infinite security - I think when things go wrong in life, as an adult with kids, it's a great and important opportunity for the adults to model how you deal with uncertainty.
Thirdly - I find myself saying "There's no such thing as a magic wand" - it's a way of saying it's no good saying "I wish..." this hadn't happened or that reality was different to what it is.
So for your daughter - I would keep reassuring her and say "Don't worry - everything is going to be OK" if she's worried about the future - and then remain hopeful and support her through to the next stages of discovering what she will do with her life - she can still carry on studying if she wants to - their happiness is important and you realise that when you are faced with real problems; my daughter fell seriously ill while at uni - believe me you don't worry about academic success at those points - I sat with her while she wrote an email to the uni saying she needed to step down from the 3rd year of a 5 year course (imagine having worked all those years to get to where she was and then to have to let it go) - in order to be admitted to hospital - she was hospitalised for 6 months - I said to her exactly what I'm saying here - "Don't worry..." etc - of course I didn't know the way forward or any of the answers at that point - I didn't pretend I did - it was just important to let her know she had the support she would need and that we would find ways. We did and we're even closer as a result.
I think it's a great shame that many students come to see themselves as successful only if they are academically successful - most teachers aim to praise effort not achievement - I wish more parents would take that to heart - so if a child doesn't do well in exams or at school imagine what that might lead them to feel about themselves. I find all children benefit from lots of honest praise about a million things other than how well they do in an exam - they can be praised for being a good friend, cheerful, forgiving, helpful, funny, a good listener, thoughtful, honest, playful, loving, good company, supportive, imaginative, hard working, accepting, a clear thinker, good under pressure, tenacious, deep thinking, a good speaker, observant, intuitive, understanding, open minded, humble, non-judgemental - these qualities really do matter in life.
Your relationship with your daughter matters a lot to both of you and now is an important time to pull together. I agree - you should still try and think of something memorable to do to make a happy memory that you can link to results day.