Your DD definitely needs biology and chemistry. Work experience, preparing for BMAT/UCAT and medical school interviews take up a lot of time, and there is little advantage in taking 4 A-levels over 3 when it comes to getting into med school so your DD might want to see how it goes with taking further maths. There is no point in spreading herself to thin and getting 4 As when she needs A*AA (for example). It can be better to concentrate on getting very good grades in 3 subjects rather good grades in 4.
Schools normally guide university applications. If she applies to med schools that use the BMAT or UCAT exams for selection, she will need to prepare for the exams herself and apply searately to UCAS. Some schools are also exam centres for the BMAT so she might be able to take the exam at school.
Work experience is also important and can take time to arrange (there are lots of students all looking for placements) so start applying now. It doesn't have to be be in a hospital or with a GP, it could be anything related to the skills needed to be a doctor eg volunteering in a care home or special school or riding for the disabled, St John's ambulance, working in a pharmacy, scientific research.
She also needs to research the different med schools. They all have different teaching methods. How much clinical experience is there in the pre-clinical years? Do the teach traditionally or mostly by PBL (problem based learning)? Do they teach anatomy by dissection or prosection? Does she want to intercalate for a year and take a related BSc (compulsory at some med schools, optional at others)? Some universities (eg Oxbridge, Imperial) have a greater emphasis on the research/academic side of medicine than others, both in teaching and selecting candidates.
It's also important to apply tactically. She needs to chose med schools with a range of different grade offers so she has an insurance offer. Different schools have different criteria for selecting for interview (GCSE grades, BMAT/UCAT, work experience) so she should reseach where she is most likely to get an interview. They have different interview styles (MMI or panel interview or both), does she feel she might come across better with a particular style? It's also worth looking at the application/interview/offer ratio for different med schools. When mine applied, St George's was the only med school that ever had places in clearing but only for applicants that hadn't been rejected at interview so it was an extra back up if you didn't get an offer.
Medical School Interviews by Picard & Lee is a good book to help prepare for interview. It's also worth picking up a book on writing personal statements for med school. Generally, med schools don't use the personal statements for interview selection but they may use them for discussion at interview so it is good to pre-empt the questions they will be asking and answer them in the PS and emphasis the qualities/skills that the schools she has applied to rank most highly in their selection criteria e.g. academic research (Oxbridge) versus work experience (St George's). NB that was correct when mine applied, that might not be the case now!
These are good sites to start her research:
www.medschools.ac.uk (The Medical Schools Council)
www.themedicportal.com
The student room is also a good place for her to talk to current medical students, fellow applicants.
Good luck!