Student or Learner
A woman went to the office block. When she was inside she opened one of the doors and walked into a cage of glass and mahogany in which, behind a desk sat a good-looking girl.
Does it mean that that room resembled her a cage? Like the one in which birds are kept for example?
Later that girl who was inside:
... indicated a leather-covered banquette against one wall of the cage and said, ‘Sit down. I may be a minute or two.’ She opened another of the cage walls and vanished.
I understand that this further context doesn't change anything? It was a room which resembled her a cage?
You understand correctly.
Perhaps metaphorically. Trapped in the corporate world, or in a job that she hated (or would have hated if it had been hers)?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.