This is a 1946 Mercury sedan, unsure of model name. The Queen is driven around in this, and it ends up in the main character's possession at the end of this story.
Cait MacReady's personal style is a little schizophrenic. When in work environments, which includes meeting clients on her own or under the pretense of representing fictional bookseller Rory Soame, she leans towards vintage looks, a little formal, maybe a little bit severe. This is armor for her, just suiting up. The dress on the left is something she would wear to a club environment (which does relate to a scene in the novella.) These are starting points. I'm not going to be a stickler because I don't know enough how to be one.
In casual settings, she's more likely to be in ratty jeans, t-shirts like the one above (which she spends the last third or so of the book in) and oversized jackets, often men's cuts/styles. Can lean towards typical punk, though by 1987, outright punk fashions of 77-83 would be a more deliberate pose. Tends to wear sneakers or heavier boots if she's not on-duty. Boots definitely if she thinks there's going to be trouble.
Datura flower, also known as jimson weed. Common enough in southern California. You may even have some of this in your neighborhood. Ariella, the Queen of the title, has a large tattoo of a datura bloom, close up, following her collarbones and dropping down between her breasts. It's a fairly extreme tattoo for 1987, but refined, very beautiful. If you want to use this element, you can go stylized/abstract, where the shapes might recall a galaxy or a swirling organic construction. But all the same, I'd prefer it to be recognizable.
Some photos from around LA to give an idea of the kinds of textures you might want to work with. You've never been shy about suggesting texture in your work, particularly in INVISIBLE REPUBLIC, so it'd be great to see some of that here, if that's an avenue you want to go down.