。
She's every bit as attractive as her older sister.
Literal
She [topic-は] older-sister [target-に] not-being-inferior [extent of-ほど] attractive is.
劣らぬ uses the classical negative ~ぬ (modern equivalent: ~ない), which survives in formal and slightly literary writing. Combined with ほど ('extent'), the construction reads 'to an extent no less than her sister' — an elevated way to assert equality. 魅力的 ('attractive, charming') uses the productive な-adjective suffix ~的 ('-ish, -istic'), which fuels much of modern Japanese's abstract vocabulary: 一般的 ('general'), 効果的 ('effective'), 個人的 ('personal').