NO-ONE is 'guaranteed an interview' on the basis of their GCSEs alone!
Your daughter will need to meet ALL the academic requirements in full AND present a decent PS, plus any other requirements (UKCAT etc) to even be considered - and she will be ranked against all other applicants for a highly contested interview place. IF she was interviewed, she would then be ranked for an offer on her interview score - and may not get an offer at all. Btw, you will not have a clue what any University's 'cut off score for interview' is, and just because a PS isnt referred to at interview does not mean it wasn't part of the selection process. Despite having (apparently) one child already on a degree course, you seem to have a very odd idea of how University admissions actually works.