May I suggest that you head over to the medicine threads on the higher education boards for reliable, informed, sensible advice? One of the posters is a teacher who is also the school advisor for medicine and vet school applications, as well as having a recently graduated doctor DD. There are lots of other knowledgeable posters who have been through the process who offer advice, as well as parents supporting DC going through applications.
There are plenty of med schools that only require biology or chemistry, not both. I suggest she researches which med schools don’t require chemistry and considers dropping it regardless of whether she has to change schools or not to be able to pursue biology. Even if there are mitigating circumstances, she might struggle to get an A with a 5 at GCSE as she doesn’t have strong foundations in the subject to build on.
I would suggest that she then contacts the admissions team at those universities for advice to discuss whether she should retake GCSE chemistry under the circumstances and what would be the best A level combination without chemistry (maths, biology, psychology, physics, further maths…).
I would also research how the med schools that don’t require chemistry select students for interview so she can apply strategically. Some will score GCSE results as part of the ranking to select applicants for interview, others only use the aptitude tests. She should apply to med schools where GCSE grades are less important.
Many students don’t get into med school the first time round but, if she can get the grades and spends a gap year working as a healthcare assistant (which will give her good insight into working in medicine, valuable experience of working with patients, and demonstrate her determination and dedication to working in healthcare), she will stand a good chance of getting in post A level. I would recommend that over graduate medicine, which is even more competitive than getting in at 18. As well as being an expensive and time consuming route to becoming a doctor!
Good luck!