What is being forgotten here is that the DD is very able. I appreciate Tizer has a hotline to employers. However like Universities, many employers will be looking beyond grades, for potential, and that, as long as she regains her confidence and equilibrium, she has in spades.
One issue with high achieving kids is that they may not experience failure till quite late on. DS was possibly lucky despite a 4xA* prediction, to receive three rejections (UCL, Cambridge and Warwick). All his peers had offers whilst he was waiting on the ever dilatory LSE. This first experience of rejection, in his eyes failure, hit him surprisingly hard, but he was still at home and had both family and school support. Things worked fine in the end. He has recently been looking for his first post PhD job, and honestly I think we were as upset as him when a couple of promising opportunities did not pan out. He remained optimistic that he would get something and he did.
There is a golden path from top table in primary to entry to a selective secondary or top sets, top grades, Oxbridge, good degree then sought after grad scheme. The process can churn out people who are perhaps less rounded or resilient than you might want. (And in some cases with a level of unwarranted arrogance. The right school and the right University does not mean that you have proved yourself.) A couple of blips en route, though painful, may actually be a good thing. Learning to accept disappointment by saying "what is the worst that could happen" and then realising that Plan B is a perfectly acceptable alternative, is a useful skill to have. What most people want is for their DC to be happy, and I have come across a few people whose DC stop for the first time in their late 20s look around and wonder whether that high paying City job or whatever else they landed at the end of the golden path, is what they actually wanted and/or want to be doing for the rest of their lives.
I asked DS, who has just completed a PhD at a high ranked US University what he thought was the main benefit from having been at a well known and very academic secondary school. Apparently it was that he was never top of his class. Indeed he started A levels in the sixth math set. In contrast many of his high flying peers both at Undergraduate and Postgraduate level have always been top of the class, until inevitably they reach a level where they are not. Often with a real wobble as they try to work out how to cope both with challenging material and with the realisation that others are more talented. DS observes them but is able to plough on. He has got a lot further than he might have been expected to, in part because his expectations were flexible and were never set at a specific high point.
I suspect that this is a real problem. Lots of big fish coming from smaller ponds, and a need to accept that rather than being the person who got to Oxbridge, you are just one of many who are at Oxbridge. Back in the real world and talented able people, including those who have learned from setbacks, are a valuable resource. The DD may not get on a top grad scheme, but once she regains her equilibrium she will be able to apply at a different/relevant entry point, explain that University had been difficult but that she now understands why, has made the appropriate adjustments, has a five year plan of where she wants to go (Open University, a year out to take a Masters with entry based on practical experience, whatever) and wow them. Employers are not just hiring the first or whatever they are hiring the person and the contribution they will be able to make to their business.
(End of rant!)