。
She's anything but honest.
Literal
She [topic-は] never honest is-not.
正直 ('honest, straightforward, frank') is a な-adjective; the negative form 正直でない is the fully written negative of the copula (modern colloquial: 正直じゃない). The omission of the は particle inside ~でない (vs. ではない) gives the sentence a slightly literary or formal feel — the standard prose negation rather than spoken contraction. In moral commentary, 決して...ない paired with 正直 amounts to a sharper character verdict than just saying 嘘つき ('a liar').