。
She's no less beautiful than even her older sister.
Literal
She [topic-は] older-sister [target/even-にも] not-being-inferior beautiful.
Adds the focus particle も to the standard ~に劣らず frame. The combined にも implies 'including her sister, who is the high standard' — emphasizing that the comparison reaches even the highest reference point. A subtle but useful nuance: a learner who only knows the bare ~に劣らず might miss the 'even' implication that も brings.