She believes that based on her expected GCSE grades that she will be unable to get into a "decent" university and that most high flying careers will be closed off to her. This is probably true. And if it is not true for her then it must, by definition be true, for the majority of people as there aren't enough high flying jobs for everyone otherwise they'd be just called "jobs"
Christ this is depressing. She hasn't even sat her GCSEs yet!
I think you are wrong on two fronts.
1. That graduate schemes are beyond those not at top-tier universities
I've interviewed people for training contracts and these days there is a lot of pressure to widen access to the professions so whilst anything below a 2:1 rules you out, as long as you clear that barrier then your CV is considered as a whole. When we interview we aren't told what university the candidate went to precisely for this reason. Of course that does get factored into the final decision but it's quite a fluid exercise - essentially you'd give pluses for Oxbridge, neutral for RG uni, minus for anything less BUT this can be counter-balanced by the rest of the CV. So an Oxbridge grad with no extra-curriculars would impress less than someone from a lesser University who'd run the student union, played a lot of sport, done charity work, loads of work experience etc... You really don't need to be a genius to be a good lawyer so anything that shows you have the other skills a lawyer needs is valuable (in the early years mainly just an ability to work bloody hard).
It's not easy (mainly because the Oxbridge grads know this and will have done lots of extra stuff too) but it is not an absolute bar.
2. Focusing only on 'high-flying careers'.
What counts as high-flying? What are we actually talking about? I suspect in this context you are using high-flying to mean well paid.
There's such a bubble around here that our children will tend to be surrounded by parents and friends' parents who work in the city. But these aren't the only 'high-flying' careers. They are the well paid ones which isn't the same thing.
There are so many fulfilling careers out there (both for graduates and non-graduates) but it doesn't sound like your friend's daughter has really considered what she wants to do. It's as if she's thought well if I can't be a banker/lawyer then next best thing is to work for one.
So even without the knowledge that her choice was also partly motivated by a completely misguided belief that this will also help her land a rich husband I would not think "sensible person".
No double standard - it is the same point. She is completely failing to think about what sort of job she might actually enjoy which should always be the key consideration.