Alcohol does funny things to us. This is essentially why we drink it. Many of these effects are positive; that said it is also unfortunately responsible for some near biblical lapses of judgment. This is because deep down inside all of us, in a place we don't like to talk about... there be monsters!
It's her day. Sure, they say that about a woman's wedding day, her quinceañera, hell maybe her last teeth-cleaning, but the difference, and an important one, is this: on none of those occasions did she find herself occupied with pushing a human the size of a young pumpkin out of her body via an egress the size of an kumquat.