。
She is very charming.
Literal
She [topic-は] very charm-like is.
魅力的 stacks 魅力 (charm, attractiveness) with the productive suffix ~的, which turns a noun into a na-adjective meaning 'characterized by, -like, -ish.' The same suffix gives you 個人的 (personal), 効果的 (effective), 一般的 (general). である is the formal counterpart to plain だ — almost exclusively written, common in essays, news, and academic prose where neutral だ would feel too casual.