Even if she doesn't know how to make a gin and tonic, you'd expect her to take a guess.
Scotch and dry I would struggle with, though. I wouldn't know what dry was. I shall google it.

Yahoo Answers can't decide. They nominate vermouth, ginger ale and "no ice". More reliable sources suggest ginger ale or similar. One high google result suggests Scotch Quick Dry Adhesive. I prefer to think she gave you that.
(sabre-tooth monkey, Wed 9 Mar 2011, 13:38, 2 replies)

Most barkeeps seem to not know what a Scotch and Dry is,
as I invariably find myself having to explain when I order one. Upshot being, that I rarely order them any more.
( monster munch person, man, woman... camera... TV?, Wed 9 Mar 2011, 15:06, closed)

The dry is indeed dry ginger ale
Maybe it's an Australian thing.

Part of what I find so funny about the story is that "scotch and dry" is more ambiguous-sounding than "gin and tonic", yet she knew how to make the former and not the latter.
(oball needs Satan more than he needs me, Thu 10 Mar 2011, 2:06, closed)

Here..
... I would ask for scotch and ginger (or ginger ale) rather than "dry".
( Ugi , it's a game of give and cake, Thu 10 Mar 2011, 11:33, closed)