Please don't take it personally, I'm sure you had good, honest intentions. The sad fact is that "showrooming" has become so common and the little mom-and-pop brick-and-mortar stores are having a really tough time competing with online retailers. I don't blame her for being upset, although she could have treated you nicer and more professionally.
Score some points with her - figure out what to do with the fabric and go back and buy it from her. Smile at her sweetly and tell her that you really DO want to support your LQS. You'll win over a local businesswoman.