Did you post a pattern that she copied ? or did you post a picture of a striped scarf and she made a similar one?
Sorry, but you can't copyright inspiration. Things are created all the time from inspiration... unless they are using someone's personal pattern and selling without their permission then there's really nothing they are doing that is wrong. A simple striped scarf is not something that could be copyrighted.. I guarantee yours wasn't the first
I know, coz I sold a TON of them last year at christmas lol Now if she's stolen your pattern and giving it away or calling it her own that's something different... a written pattern, not an idea for a striped scarf.
I understand why this might bug you, it probably would me too especially if she had the cheek to admit she was going to take the idea and sell it on ebay. That was just rude... but she's really done nothing wrong to be honest. Rude yes, illegal no.