。
She read the bestseller right away.
Literal
She [topic-は] bestseller's novel [object-を] right-away read.
早速 ('right away, without delay') is a Sino-Japanese adverb that emphasizes prompt action — common in business correspondence (早速ですが 'getting right to it') and narrative reports of swift response. ベストセラー is a katakana loanword; the modifier-modified order ベストセラーの小説 ('a novel that is a bestseller') uses の to attach the loanword as an attributive descriptor of 小説 ('novel'). The plain past 読んだ marks completed action.