If she says she is sick she needs a doctor's certificate... otherwise she may be in trouble with BOS
If she wants to have minimal impact on other people's marks, she has to go into the exam and leave without answering a single question... this is pretty much the only way to be considered as an outlier and thus be removed from the schools scaling. Should she attempt more questions and get a semi-reasonable mark, she will not be excluded and will pull everyone else down as a result.
However before doing this, she MUST check that she is the only person doing this... should a friend join her, their marks will be counted as 0s and the whole class will be pulled down as a result - in this case she has to study or put everyone else's hard work in jeopardy.