DS was considering applying for economics at Cambridge last year. He went to the open day, and the advice he was given there was pretty much what he had been told by a family member who is a professor in a different subject at Cambridge, as well as school staff: Cambridge (much more than Oxford) looks very closely at actual marks in AS levels, and unless you have an average of at least 90% UMS in all relevant subjects, preferably over 95%, there is little chance you will get called for interview. If your DD's school does not have much history of sending students to Oxbridge, they may interview her with UMS closer to 90 than 95, from what I've heard.
I know that AS exams changed this year, but did you still get given breakdowns of your marks in each paper? If so, I presume Cambridge will still be more interested in those than in predicted grades.
Also, DS was strongly advised not to drop his 4th A-level subject, as he was doing maths, further maths, history and economics, and while Cambridge economics sees further maths as very desirable, they don't seem to like it if maths makes two out of three of your A-levels.
Looking at average UCAS points for people who get into Cambridge to do economics, they seem to be well over 600, which would suggest that most people are doing 4 A-levels (and getting A*s in them), plus EPQs, further maths qualifications, high grades in musical instruments etc which add up to further UCAS points.
DS ended up not applying to Cambridge, as he mucked up a couple of his AS papers so didn't have the required UMS average. He did much better in the A2s, so has the grades for Cambridge, but by then had lost interest in Cambridge so is off to Warwick.