It depends on which courses you are interested in but for academic courses at the established Universities the offers will be on specific grades in specified subjects not UCAS points.
As far as studying an additional GCSE subject because it is an area of interest I would say that GCSE study is not the best way to develop a general interest in a area as they tend to be rather limited & prescriptive.
Yes, I agree, and am opposed to her doing it. However, I need hard evidence to suggest that the subject is a WOT and will not be valued by universities. Because it is a science, and she is interested in sciences, she feels it will be worthwhile whatever. No words from mother can persuade her; but something on an official website just might.