The simple answer is no. If she gets A*s in all other sections she should be fine (gulp).
However....
Ok, I don't know which exam board you're referring to, but will assume it's AQA (as that's the most common one). It really depends what assessments they actually were. I know you've said they were worth 15% of the overall mark, but there are a couple that fall into this category i.e. were they worth 15% each, or were they worth 15% combined together (just checking, because it is confusing!)?
I suspect you're talking about the Language GCSE only (Literature has only one CA, which is worth 25% of the overall mark- it's the one that involves a comparison with a Shakespeare and something else), in which case you are only talking about one GCSE rather than the lit and the lang. I'm also guessing that you're talking about the creative writing component, which has two parts to it.
Technically she cannot do it again. However, I'd be interested to know what is meant by the 'practice' you're talking about because I'm not quite sure what the school was doing and don't know the full situation...PM me if you want to know more about an area that some schools are treating quite hazily.
- I'd be really worried about why she got so nervous. There are some really hefty CAs in English, as in all the subjects and she has got nervous on two of the less significant ones. Have to say we are also regarding these as being the most straightforward ones in English. I'd be really, really worried about making a fuss as it may make her more nervous for more important CAs. And what about the exams? Why has she got so nervous for these two?
- You could write a polite letter of concern to the school. There are different options for CAs and the school is obviously running them in an 'exam style'. You can actually sit them in quite a relaxed fashion over the course of a series of lessons. If you feel that this would be more appropriate for her, perhaps say so now. We would certainly make allowances for this.
- The school is learning and, probably, a little stressed. We're all worried that this is a guinea pig year group and nobody really knows what they're doing with the CAs. In our school we will actually be running them more 'exam style' next year, as our students haven't taken them seriously at all. Wish we'd had a single one who'd reacted in the way your daughter did. I've spent most of the past month patrolling the corridors during Year 10 lessons with a trail of naughties behind me. I've had to remove an average of 15 children from our 14 sets each period for distracting others!
- AQA have told us emphatically that we should not give out letter grades to students and, in fact, the marks we use to assess students come in bands with numbers attached. The school is only guessing the grades- they can work it out roughly, but this is not definitive. Whilst I understand that the grades were criterion rather than norm-referenced in the past, I don't think we're fully sure what they're going to do this time.
Get her to relax over the hols.