re: The main villain for season three of Arrow

It's definitely as good of a guess as any with her showing up in the Flash episode that introduces to the show. But they would have to explain in her flashback episode why she changed her name. And if Captain Cold is her brother, then that means they were planning on putting him in Arrow since I don't think the Flash show was a go during season 1.

And yeah, they could (and would) introduce her without giving her those powers.