This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
媄 combines 女 (woman) with 美 (beauty). The exact historical development is uncertain, but it likely relates to feminine beauty.
A woman 女 beside beauty 美 suggests a beautiful woman, but the kanji's meaning is not firmly established.
For ビ, imagine a beautiful woman named Bea: Bea -> ビ, and her beauty is the focus of 媄.