。
She stopped looking at the shop window.
Literal
She [topic-は] show-window [object-を] looking [thing-of-の] [object-を] stopped.
A clean example of ~のをやめる ('stop doing X'). The verb 見る is nominalized with の and made the object of やめる ('quit, cease') — turning an action into a thing one can stop. Note the long-vowel mark ー in ショーウインドー standing in for ウ; both ショーウインドウ and ショーウインドー are accepted spellings for the same loanword, with the chōonpu version slightly more common in casual writing.