。
She's just as good-looking as her older sister.
Literal
She [topic-は] looks [point-of-の] [point-では] older-sister [than-に] is-not-inferior.
器量 in this context refers to physical attractiveness — particularly when applied to women in older or more formal contexts. (In other contexts, 器量 can also mean overall capability or character — the 'measure' of a person.) ~の点では ('in the point of, in terms of') is a stable formal-register collocation for narrowing the scope of a comparison. 劣る ('to be inferior') takes に for the standard of comparison: AはBに劣らない = 'A is not inferior to B,' so by litotes, 'A is at least as good as B.' This is a softer, more elegant way to compliment than directly saying 同じくらいきれい ('equally beautiful').