I have 2 meters and I posted the results of a test from the same sample the other day.
Accu check mobile = 4.8
SD Code Free = 5.7
Given the accepted margin of error both reading are acceptable. In your case neither you meter or hers are right, nor are they wrong. As I have posted many times before don't read too much into an individual reading, but look for trends over (say) 7,14,30,90,180,365 days
And as many post here, and IMHO the best advise "Eat to your meter"
@Indy51 posted a link to a Micheal Moseley talk the other day in which he talks about his training. He was told that over the next 5 years they would learn an awful lot, but that in 5 years time it would be out of date. Seems your GP is living in the past
Leaching was good practice in the 17th C