There is no hidden agenda at medical schools, if you meet the entry requirements they will not treat you any differently whether you did Maths/Bio/Chem or Art/Bio/Chem.
DS1 did Maths/Physics/Chem and said that he has used his A level Physics at St Andrews, but most won't have done it. Maths/Physics knowledge is needed for BMAT at GCSE level, but people who have not done Physics A level find they are a bit rusty. Apart from giving a BMAT advantage, Physics will not make a difference to her chances of getting in.
I would agree with the school that Physics without Maths makes it harder to get the top marks. DS2 says about 5% of the exam questions use maths knowledge which is taught in Maths A level and at his school the Physics teachers did not cover it as they assumed it had been learned in maths (eg logs), there is also a significant overlap between Mechanics and Physics.
The best subjects to choose are the 3 she is really confident she can get As in.
The subject requirements are:
Chem + 2 other sciences (Bio, Phys or Maths)
Most Cambridge colleges
Bio and Chem + anything else
Aston
Birmingham
Brighton and Sussex
Cardiff
Edge Hill
Exeter
HYMS
Imperial
King's
Lincoln
Nottingham
St George's
UCL
Chem + 1 other science (Bio, Phys or Maths) + anything else
Aberdeen
Bristol
Buckingham
Dundee
Edinburgh
Glasgow
Liverpool (3rd subject academic)
Oxford
QUB (need AS Biology if don't have A level)
St Andrews
UCLAN (3rd subject academic)
Bio + 1 of (Chemistry, Physics, Psychology, Sociology, Environmental Studies or Geography) + anything else
Southampton
Bio + 1 of (Chemistry, Physics, Maths or Psychology) + anything else
Plymouth
Bio or Chem + another maths/science + anything else
ARU
Leeds
Barts
Sunderland
Bio or Chem + another maths/science/psychology + anything else
Manchester
Sheffield
Kent and Medway
Leicester
Keele
2 out of (Bio, Chem, Psychology) + anything else
Lancaster
Bio or Chem plus any other 2
UEA
Any 3
Newcastle