Princess, have you ever grown sweet potato vines? They're really fast-growing and very leafy -- with several of them, say 3 or 4, spaced across the width of your window and a stick/post on either side of the window, then a couple of rows of twine or heavy string tied to either side. They like water getting started but are pretty hardy. When winter comes, pitch 'em out and start again next spring. Or some other fast-growing vine that likes your summers.
Hmm. That leaves your window undressed all winter, doesn't it?
Little pickets? Actual shrubbery? Curtains on the inside? Blinds on the inside?