A2 grades

Hey! I am doing AQA A level Biology, Chemistry and Psychology and once I finish school I want to get an apprenticeship at a pharmaceutical company and last year they just asked for 2 A level passes in science subjects but this year they are asking for a C in Chemistry and another science subject. Once I done my AS chem exams I went through them with my teacher and when she added up my marks she said I might get a C but when I got my results I got a D but didn't send off for a remark because last year and previous years they have only asked for a pass in chem. Would it be possible for me to go from a D to a C at A2 with a unit 2 and ISA resit? My teacher said that I would never get a C (basically because she thinks I'm stupid) but she had put me in for the resits before christmas and I only found out the requirements this week. I feel because she's saying I can't get it that I won't get it but I want to know if its possible to go up a grade with the resits I am in for? Thanks for any help