The school is right about the regrade. BUT and this is a big but they have discriminated against her because of her disability.
The very minimum they need to do is allow resits with the adaptations and they should also be writing a big cheque to her.
She is probably better off at college / FE / Adult Ed. If possible she should do a three year VI form, start taking AS courses but with maths and English along side.
I'm dysslexic and use a blue background and it makes such a difference.
Another option is to go for November resits, this may be with a different exam board, edexcel do resits in November for maths and English.
I'm quite bolshy, I'd write to the school, tell them they have acted illegaly and what you want to put this right.
Things I would ask for
Them to pay a private tutor for each subject.
Them to pay for entering her for resits, either at the school or elsewhere.
The cost of keeping her for a year (if she does 3 years), and a payment for hurt etc.
Do you have legal cover on your house insurance?