feedsack

A sack (bag) for feed, usually of cotton or polymer cloth or of heavy paper.

He brought us his fruitwood sawdust in an old feedsack, ready to be used in our crafting project.

Sackcloth. (In the nineteenth and twentieth centuries, feedsack cloth was often reused for making clothing, quilts, or rags, and this tradition continues to some extent today.)

Near-synonyms: hessian, burlap

Let's be honest: the outfit hardly matters — you could put her in a dress made of feedsack and she'd still look fabulous.