Hi Lesley, and welcome to the Forum.
If she does miss out by a couple of marks on the second test then it would certainly be part of the evidence needed for an Appeal. Obviously the mark for the other paper plays a part too, and all successful Appeals are based on strong academic evidence first and mitigating circumstances second.
As the Head was invigilating, he himself saw what happened, and should be able to document it for an Appeal. Even an anti-Grammar Head should be able to bring himself to write a factual statement!
There is nothing that you need to do now apart from wait as patiently as possible, along with the rest of us.