。
She categorically declared that he was dishonest.
Literal
She [topic-は] he [subject-が] dishonest [quotative-と] asserted.
断言する ('to assert categorically, declare') is a strong, formal verb of speech with no hedging. The 不- prefix on 正直 negates 'honest' — a productive prefix used with na-adjectives and some nouns (cf. 不安 'uneasy,' 不便 'inconvenient,' 不可能 'impossible'). The と marks the asserted content.