The major difference is that only some insignificant weirdos in the fringes have not agreed that communism is stupid in practice. Brutalist aynrandian ideology is much more prevalent problem and needs to be somehow gotten into same ridiculed state as communism as an actual feasible ideology.
a) You're spot on she didn't want to destroy the govt. She was explicitly a minarchist, and she swapped major arugments and ridicule with the Ancaps of the time (like Murray Rothbard)
b) The communism hate gets floated most, but my read of Atlas Shrugged was that she placed the collectivists at the same evil level as the church, crony capitalists, and postmodernists, to the point of having characters who 1-dimensionally represented each of them (she's literally got a lobbyist character called "Wesley Mouch").
That's why it's always hilarious to me when I see neocon congressfolk saying that Atlas Shrugged is their favorite book: she hated the church as much as the government (and would've likely hated those politicians as well).
Poked around some articles after writing some of this, found this one to be pretty neutral and illustrates my point a little better: https://www.ncregister.com/daily-news/the-paul-ryan-ayn-rand...
It seems to me that Ayn Rand / Atlas Shrugged get used to justify a lot of brutalist ideas, even among her direct inheritors. Having watched some of her interviews and read several of her books, I'm not convinced that the elimination of government was her intent. Further, while she tried to paint a realistic picture, ultimately Atlas Shrugged is a work of fiction that falls apart when placed within real-world constructs, especially 50+ years on after its publication.
At the heart of it, what Rand appeared to most argue in Atlas Shrugged was against regulation and governance that superseded the inalienable rights of citizens plus centralized power in an authoritarian state and took away the economic agency of the individual. That doesn't preclude a functioning republic where people can own businesses, own the rights to their creations, and still pay taxes for the benefits of services best provided by government.
Now here's the irony: Rather than coming for our system via communism, which was Rand's concern, instead it was nominal capitalists who came to destroy the system via regulatory capture. I don't see what the right-wing, nominal capitalists in the US have done to be any different than the moochers in Rand's book.