She is gloomy about the C but I think she could always drop it. Her main problem is that her subject requires three A's or AAA.*
If I recall correctly, she wants to do maths/physics. For these subjects it is true that the typical RG offer is three As or two As and one A star. However, as said on many threads, outside the top 5-10 universities, RG typically accept one or even two grades below published offers for these subjects in August. This is particularly true in physics, for which recruitment is a problem - and many physics departments are under massive pressure to improve their gender ratios so would be very reluctant to turn away a near miss girl.
There is a major gender problem for maths, physics and engineering undergraduate applications. Boys look at the three A or higher requirements and happily apply/accept offers when their predictions are barely at the required level. Girls are much more cautious and play it safe - and accordingly end up at weaker universities than they should. If she gets AABC in AS, with AAA or AAB predictions for her three A2s, then she should be applying to good RG university courses, safe in the knowledge that she will be accepted by at least some even if she drops to AAB.
She should absolutely not be applying to places with published offers of AAB or lower for maths/physics, as this means they will be filling places in clearing at BBB or perhaps even lower. If she looks like an AAA candidate then she is too strong for these courses.