。
She's not selfish at all.
Literal
She [topic-は] never selfish is-not.
わがまま ('selfish, self-centered, willful') describes someone who insists on getting their own way — a child throwing a tantrum, an adult refusing to compromise. As a な-adjective and a noun, it functions as both a label and a description: わがままを言う ('whine, demand willfully'), わがままな子 ('a willful child'). The adjective is sometimes written 我儘 in older texts; the kana spelling is now standard. 決して...ではない here defends her against the charge.