When a baby is formed, for the first trimester it is actually able to take care of itself. That doesn't mean you can eat, drink and be merry though! You have to look after your body because if your body is in a bad state then it won't take the placenta, which forms in the first few months. But a bit of alcohol and some no-no foods (providing they don't make you really sick) aren't a problem.

The little egg has loads and loads of nutrients in. The baby initially just makes hundreds of cells without growing, then starts to grow using those nutrients. After about 8-10w they need a bit extra and as the placenta is grown by then it can take some from the mother - the placenta isn't fully formed so the stores from the egg are still being used. About 12-14w then it's nutrients from the mother only.

5-6w and what you do to your body won't directly affect the baby, but could the placenta. The food rules are to stop you from getting sick from bacteria which could be present - if your friend is well then it's not a problem at all. The alcohol can affect the baby a bit, but not at this early stage. As you say, your friend just had a couple, not blind drunk drinking, which isn't at all harmful (I had the odd drink throughout pregnancy - never more than one at a time and never more than 2-3 a month, but I was comfortable with that; having said that, DS will drain an unattended wine glass if he spies one, luckily for him I never leave more than a drop of wine in an unattended glass!).

HTH!