Private candidate but still in school

So my HOY will not allow my computer science teacher to predict me an A because of my mock grade despite him wholeheartedly believing i can achieve the grade. I’ve spoken to my HOY so many times and even got my mum to email but she won’t even budge to a B and will only predict me a C. my top choice needs AAB contextual and ABC obviously doesn’t meet that so my cs teacher has offered to help me apply independently. He said he could write my reference and add my predicted grades as long as the school doesn’t find out. Do you guys think this is worth it? or do i carry on with my school application with ABC and hope for the best?

Why is your HOY predicting you a C?

She's the one that inputs the grades on UCAS so she's able to override what my teachers think based on her opinion/mock grades

What subject does she teach usually? Does she actually know what you are like as a student?

She teaches Sociology. She's never taught me before so has no idea what i'm like as a student however she even told me herself that all my teachers have said i'm an amazing student and a pleasure to teach

Right okay, I would make a complaint to a more senior member of staff in your sixth form if possible, because it doesn't seem she has any sort of qualification to change your grade from what you have told me.

Unfortunately she is the most senior member of sixth form. I don't know who else I can speak to because the other 2 members of the sixth form team are less senior than her so they can't really do much.

Unfortunately she is the most senior member of sixth form. I don't know who else I can speak to because the other 2 members of the sixth form team are less senior than her so they can't really do much.

Go to her line manager or the Head if necessary. A HOY has no authority to change predictions! I've taught in three schools and have never heard such nonsence.

My internal UCAS deadline is tomorrow so idk if i can do much before then