。
My sister's eyesight is perfect.
Literal
Younger-sister [possessive-の] eyesight [topic-は] nothing-to-complain-about.
申し分ない ('impeccable, nothing to complain about') is a set expression — 申し分 ('room for complaint') + ない ('none'). It's a refined way to say 'perfect' or 'flawless,' more elegant than 完璧.