Well last weekend my Dad was in Paris on the "lad's weekend" for the France-Wales game. At one point they were in a bar with a group of acquaintances or friends-of-friends, including a journalist for the Western Mail who was staying sober in order to write up his article. So, for this round he asks the girl with him to get him a coke.
Five minutes later the waiter plonks a cheese and ham toasted sandwich down in front of him, which is stared at in bemusement by all at the table. "Did you ask him to get me 'Un Coke, Monsieur'?" says the guy. The girl agrees. "I thought so", he says, "this is a croque-monsieur."
(The owner was puzzled at the gales of laughter coming from those strange foreigners in the front of his bar).
 In this case, girl could refer to any female up to about 35 years old.