I think it depends on what you're trying to prevent. Flu vaccines have to adapt to rapidly evolving new strains every year, but you would still be immune to the specific strain in the vaccine for a long period.

Yea starts waning after a year but there is a phenomenon called back boost is that if you get reinfected a year later with another variant, this still boosts antibodies to the variant of previous infections/vaccs. I suspect she might not have conditioned to select individuals with no recent infections. Also happens in regular vaccines (maybe less in magnitude than mRNA, that I don't know). Without this memory we would be toast and this lady does not even know this or does not know statistics. I hope she is not in some serious capacity for making healthcare decisions.

Yeah, I didn't know that. I'm glad I'm protected for longer. Thanks modern medicine!

One year is more like the protection is so good that you probably won't even get sick.

I think it also depends a lot on the vaccine though. Something like meningitis or the MMR seem to be much much longer lasting, when you've had your shots you don't need them again.

Probably someone who knows more about vaccines can explain it better.