I thought the one year thing was to do with school league tables rather than that it affected individual students? I may be wrong here...
it doesn't always affect the individual student, it depends how strict the school is, or how competitive the course is
If your daughter is only 12, she has plenty of time to choose another few GCSEs to add to her repertoire if she wants to do so - I’m sure she will do well. Will she go to 6th form or study A Levels at home too?
we don't accept students who have done this into A level.
It is very easy to get 10 top grade GCSEs if you sit them individually, and very much harder if you sit them together, so this is why often only GCSEs sat together are counted.
We only accept A level students who have sat a minimum of 5 altogether in one sitting, including English, maths and the subjects chosen for A level.
Some universities allow split sittings on some courses, some don't, but for competitive courses like medicine, sitting only 7 at once, then others later will be a distinct disadvantage