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She talks about that as if she knows everything there is to know.
Literal
[topic-は] just-as that thing [about-について] anything is-knowing-[as-if-かのように] talk [object-を] does.
そのことについて ('about that matter') uses について ('regarding, about') — a compound particle marking the topic of discussion or thought. それのこと would be redundant; その modifies こと directly to give 'that matter.' 何でも ('anything, whatever') paired with 知っている gives 'knows anything [there is to know about it]' — stronger than 知っている alone. The まるで~かのように simile makes it clear that her show of expertise is unwarranted: she's talking as if omniscient, not actually being so. A thinly veiled criticism of pretentious authority.