。
She hung beautiful curtains in the window.
Literal
She [topic-は] window [on-に] beautiful curtains [object-を] hung.
カーテンをかける ('hang curtains') uses かける ('hang, put on, install') — a ubiquitous and surprisingly versatile verb that covers hanging things on walls, putting on glasses, casting spells, making phone calls, and many more. The window is the location/destination, marked with に. カーテン is a katakana loanword from English.