You said yellow fluff? Red sexlinks are sex linked, if she was a red sex link she would have been reddish as a chick because she is a female, if she was a red sex link and was white then she would be a rooster.
If she was a yellow chick then she is not a Red sex link. What is the name of the feed store? If it was a local store that breeds their own birds she might have been the result of breeding two RSLs, or she could just be another hybrid. Sexlinks are hybrids and if you breed two together the chicks will not be sex linked.
Here is males vs female RSL chicks
Thank you all so very much! She’s a hoot and a half. When she first started developing and I knew she wasn’t a Orph I freaked out a bit thinking she might be a Roo. I’ve had no luck with Roo’s. She laid very young. I was very relieved when she popped out that little chocolate nugget!!!