Are there any Fine Art teachers here who could explain a GCSE grade?

[FiveHoursSleep]

My daughter did GCSE Edexcel Fine Art and received a grade much higher than her predicted grade ( 9 vs 5/6).
I wrote to the school asking how this could happen as we had a lot of stress around the subject over the last couple of years, and the teacher was always telling DD her work wasn't good enough.
I have had no explanation from the school and won't chase them for answers as DD has not gone back for 6th form, but I'd love it if someone could explain how this can happen in a subject that is all course work.
Her portfolio was not one that was assessed either- she had predictions of 5/6 s for most of her work for two years and then when she got her mark before her written exams it was obviously very high.
Not everyone in her class got unexpectedly high grades but some who were predicted 7/8 got 9s as well.