I don't think that is reasonable at all. Were you given an original deadline? Is this the first time you have been told of a deadline? Have you got many frees between now and Friday, if not, when does she expect you to do it? Do you have a good relationship with your head? Is it worth going to see the head first and explaining the situation showing that you have expressed your concerns and asked for help. No one can criticise you for that. Explain that while you are not refusing to do it, you need a reasonable amount of time to complete the work and you have asked for help - after all, you wouldn't want to disadvantage the candidates by marking it incorrectly. I suspect that this 2 i/c is in a panic and trying the bullying/threatening tactic. Call her bluff...go to the head first!