I think it means that, although she is heavily-built, she is not very tall. A banquette is a built-in bench seat against a wall or in a corner, with a free-standing table. Here's a pic of the seat part. "Winkled," I figure, means crowded in behind the table.
![](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSRpCMT99xDZAo3eH_RfrwLXhwehgOCDodVPQhJ3zk884InzaoO)