。
She's a mean woman.
Literal
She [topic-は] mean-woman is.
意地悪 ('mean, spiteful, ill-natured') is a な-adjective that here pairs directly with 女 to form a tight noun-noun compound 意地悪女 ('mean woman') — Japanese frequently fuses adjective + noun this way without の. Compared with the i-adjective 悪い ('bad'), 意地悪 zooms in specifically on willful unkindness rather than badness in general. The blunt copula だ ends with no softening — a flat character verdict.