She understands risk very well but doesn't have the contextual knowledge that say, a professor of epidemiology might. Or the entire medical profession, actually.*
The entire medical profession isn't quite right. Many individual clinicians will green light the odd glass of wine. My midwife did last year, many GPs do routinely. The advice a clinician gives a individual can be different to general advice, this is based on their own risk assessment.
What you're talking about is guidelines from medical bodies and groups. These will never suggest 'safe' drinking because this is very easy to misinterpret, and if just 3% of pregnant women misunderstand and drink excessively you will get some tragic outcomes.
But there is research, highlighted in Oyster's review, that suggests there is no risk associated with actual very-low (less than 2 units once a week) use of alcohol after the first trimester.
Think about it, when the guideline was 1-2 units once or twice a week, was there an epidemic of FAS disorders? No. Is it worth health bodies saying 'no, never' to prevent tragedy by an unclear message? Probably. For women it remains an individual choice.
I did drink a very small glass 5-6 times after the 1st Tri, I reviewed the research and felt very safe doing so. For what it's worth (very little), I'm a nurse, and my pregnant friend who is a doctor agreed and did the same. Infact, everyone in my NCT had before we met eachother.