A really simple idea - maybe she drinks not so much to get drunk/tipsy, but because it's the done thing - she was brought up thinking that one always should have a drink in the hand, and a particular drink at that. (Brandy and soda, gin and tonic...)

So if she's somehow persuaded (by the example of a Royal or someone else famous) that the newest "in" drink is a Pink Fluffy Unicorn, which by chance happens to be non-alcoholic, she might well drink as much and yet be much less affected by alcohol...

In other news, I'll be having a friend down to visit later this year who specifically seeks gaming sessions. I really should have you over for dinner again one night...