Congratulations on the great test scores! Obviously she's worked hard.
And now for some unsolicited advice. Having just come from a career of over 20 years with a major university, with roughly half of those years in student affairs, I can offer this as far as my experience in the US higher ed system (for what it's worth):
The "culture" of the institution is going to come into play during the application season. Some of them want only the best of the best, GPA/Scores-wise. Period. Some are looking for a more well-rounded experience from their incoming cohorts. But they all look for the value-added component. The admissions people know that students from upper-middle class families often have been bought extra tutoring and have gone to high schools that were affluent enough to be able to offer all the AP courses (in classes with equally as advantaged students - nobody not up to speed, to drag the class down), etc. The "better" higher ed institutions are inundated with applications from students with great GPAs and SATs, and occasionally family money (for endowments, etc. - hey, it happens). An applicant better have something special to offer, in addition to the numbers, that makes them stand out from the rest of the mob.
My experience is that admissions people do look at GPA & test scores, although test scores are losing favor at some universities as they don't seem to be quite as accurate at predicting success as one might hope. My institution used them in combination with the GPA to draw a "cutoff" line below which they would not usually consider an application (without there being extenuating circumstances). We had over 75,000 (yes, seventy-five thousand) freshman applications a year, and a very large percentage of them met the scores cutoff. So, once the benchmark minimum GPA/test scores line was crossed, the admissions committee looked at what else a potential student would bring to campus to enrich the campus culture. Ethnic minority (American Indian, Black, especially)? Refugee? Other hardship background? Heavy public service commitment (lots of volunteer work on the record, over several years, or political activism)? Stellar athlete or artist? Admission was not governed solely by GPA/test scores.
And then there's the admissions essay - whether the admissions office is reading 75,000 of them or just 5,000 (or 500), an essay had better have some content that stands out. It's not just a matter of it being a well-written response to a prompt (if one is given). It is pretty obvious which essays are written by the students, from the heart after due consideration, and which have been heavily edited by a hired gun or their parents. (Seriously, it shows. Admissions committees have seen it all.)
I understand that the essays most well-received at my former institution were from kids who were forward thinkers for their age or whose essays indicated they had been forced to do more to get to the point of applying than the "usual" applicant. They'd played with chemistry sets as a child, worked summers in a research lab throughout in high school, and were convinced they wanted a career in that field. They had survived a major life crisis (homeless, serious illness, orphaned, impacted by a natural disaster). They were going into nursing after dealing with seriously ill family member for years. They were ex-military (not often, but more often lately). They were the first in their family to apply. (Etc.) The campus was looking for "diversity" of background and experience - the interaction between the students was looked on as being as important in the educational experience as sitting in a 200-seater lecture hall listening to someone drone on. I'm not sure how important that is to other universities, but I'm willing to bet that the better ones do bring the "what else do you offer" component to bear when making an admissions decision.
Digression: We always ended up with a large dollop of "the usual" upper-middle class generic kids (4.5, high testers, etc.), but also a sizeable proportion of "diversity" enrollments. I remember hearing about the one who wrote in his essay of working before and after school, weekends, and summers picking fruit with his family, who were not native speakers of English. He had good, though not stellar SATs and a good GPA (few AP courses - none available), but his essay read as if he had really thought about what he wanted to say. He was the first of his family to attend high school. I believe that he also served as a peer tutor at his local high school, working with kids who otherwise would not be able to finish their diploma/get GEDs. (When he had the time is beyond me!) If I am remembering correctly what I heard, he wanted to be a doctor so he could go back to help his community. I certainly would have put him as one of my top-ranked "recommend" cases, above all the kids who were in the honor society, played lacrosse, were on their school newspapers, and active in their church, etc. Those are a dime-a-dozen. This kid knew the meaning of truly hard work, and bucked his cultural tradition to do what he had to do, with great personal sacrifice, to get to the point that the "usual" kids pretty much got to by default. I really do wish I knew how things turned out for that young man. I know he was offered a spot and did enroll. I hope he made it through.
So, un-digressing back to the unsolicited advice: What that all has to do with the UK university system - who knows? Just consider it a cautionary tale about great grades and stellar test scores. If there's only one place available and there's two applicants with great grades and stellar test scores there has to be something that tips the balance in favor of one or the other. What else does your student offer that the institution will find attractive?
My only other bit of advice is: don't push a kid to attend a school simply because "it's one of the best" or if they don't have a clear vision of why they are going into higher ed. They should look carefully at the campus culture and the actual mission of the institution and make sure it's a fit with their interests and their personality. Are they going for a "well rounded" experience, or are they going to use it as a stepping-stone institution to graduate school? (Seriously, some post-graduate programs are really picky as to where you earned your undergrad degree, so if a student has a specific professional/PhD degree in mind, it might do to see where they might want to earn it and then see where that institution's students earned their u.g. degrees.)
I listened to so many kids over the years who were at our uni because it was expected of them - and they were miserable. They put on a great show when mom and dad showed up on visitor day, and were in tears in my office the next day. I also more than once had a kid tell me in their senior year that they'd just found their true calling - and that they'd wasted the prior 3 years (and their one shot at an undergrad degree) studying in the wrong field. And there was the sophomore who showed up to my office and proudly announced they were going to major in business (we didn't have a business major), and the one who was going to do musical theatre (we didn't do musical theatre, just experimental). [Sigh] And there were those who just were floundering as one face in a 25,000+ sea of faces who would have been much happier at a much smaller institution.
And, a gap year isn't a bad thing, really, sometimes.
