ameliah123 I hope you got this sorted.
I just want to reassure you that schools CAN and DO exercise discretion. My DS was desperate to do A level physics but only got a C in core and additional science! We thought it would be a flat no on application but after looking at his individual unit modules they have allowed him onto the course. He is under the microscope though and if it doesn't work out he will move to either applied science or take up access course or do a completely different A level instead. (We are still working on our plan B)
It might be that you could ask the school if she could trial the A level chemistry and if it doesn't work out then do A level applied science? If you explain what degree course she wants to do then the school can see why it's important and possibly help with suggestions?
There are science access courses about which I think are 12 months. But, when we were looking at these we've had it explained to us that they are really mostly suitable for D and below level students and if someone got a C/B then they are more likely to take a step back with this.
I didn't even know about these but my DS was prepared to do a science access course and then to science A levels at 6th form next year. It means delaying by a year but he was happy to do this rather than completely changing his career goals.
I've also been told by a private science tutor today that he does not recommend re-sitting GCSE's or doing Access courses unless you really have to as the A level is so different in sciences.
Hope this helps but I'm scrabbling about myself at the moment trying to understand the science syllabus, degree entry level requirements, alternative routes etc and just simply sharing out experiences to see if there is anything you can use. Have you spoken with the school yourself rather than via your DD? (I had to go in myself to have a proper conversation :( )