Have you / has she looked at the entry requirements of her chosen sixth form, and any additional specific requirements for the subjects she wants to take for A Levels?
Usually thar information is available on the sixth form's website.
Example:
My daughter did A Levels in Art, Classical Civilisation, and English.
The sixth form college's general entry requirements were that she needed to have at least 5 GCSEs at grade 4 or above included English Language and Maths.
The subject specialist requirements were:
Art - to provide a portfolio of mixed media if you haven't taken Art as a GCSE
English: GCSE grade in English had to be 6 or above
Classical Civilisation: none
Daughter met those requirements and thus got in.
It doesn't sound as though your lass has much to worry about, but do log onto the sixth form's website to check it out for peace of mind.