C3 is an A2 module, is her school doing the maths A level in a year?
My DS is doing further maths, I'm not too sure I understand how the various modules work. I know C1 and C2 have to have the grades given to Maths and that Further Pure needs to have the grade given to further maths but from what DS tells me the other three modules (Mech1, Stats1 and Decision1) vary depending on their grade, they can attributed to either and that is decided by the college to maximise the maths grade even if that drops the further maths grade.
I think some schools/colleges teach maths in Y12 and further maths in Y13.