Is it the actual subject or the teacher that she dislikes? I loved biology in GCSEs and got an A in it, went to college and took biology Alevel and couldn't crack it, the teacher was lovely but she just couldn't teach me biology. I ended up completely failing first year and took an EPQ in second year instead. Is it possible for her to change teachers as she may not like biology either due to the teacher or the teaching style. It is odd that the school won't let her drop it, I know she missed the deadline but in certain circumstances from my experience the school will try and work with the student. I suggest maybe looking at a new college or school and see if she can retake her Alevels with a different subject, or looking at BTECs or apprenticeships.