Quote 19
She hummed to herself, swigged brandy, she leaned constantly forward to peer out the windows, as if she were hunting an address – or, I decided, taking a last impression of a scene she wanted to remember. It was neither of these (18.11).
The narrator wants to believe that Holly wishes to solidify her memories before leaving for Brazil, but this is his desire, not hers. Fixed memories would signify something too permanent for Holly, and this just isn't who she is.
Quote 20
The owner of the brownstone sold her abandoned possessions, the white-satin bed, the tapestry, her precious Gothic chair (19.1).
Holly leaves so most of her (already few) belongings behind when she escapes to South America. She's unencumbered by possessions, and even the things that would suggest a degree of permanence in her life get sold. Her consistent lack of furniture, and of "things" in general, symbolize the transience of her life.
Quote 21
Afterwards, avoiding the zoo (Holly said she couldn't bear to see anything in a cage), we giggled, ran, sang along the paths toward the old wooden boathouse, now gone (7.2).
Holly's resistance to being confined extends beyond people to include animals as well. While some may see the zoo as a place to learn and interact, Holly sees it as a prison.