。
She's by no means a fool.
Literal
She [topic-は] never fool-person is-not.
ばか者 ('fool, idiot') compounds ばか ('fool') with the agentive suffix ~者 ('person who'), giving a word with a slightly bookish or dramatic feel — the kind of label a stern parent or fictional villain might use. Compare to bare 馬鹿, which feels more conversational, or the harsher アホ in the Kansai region. The structure 決して~ではない again rules out a category outright: 'whatever else she is, she isn't a fool.'