Start with A Game of You. That was made for new readers, I think. It was the first arc that didn't have any aspects that relied on past DC continuity. Sure, Barbie (the main character) appears before that in The Doll's House, but there's no need to mention that.
Try getting her started with some of the short one issue stories. The introduction of Death, the one with the immortal guy, Midsummer Night's Dream, Dream of a Thousand Cats... there's a lot of good stuff there that would keep anyone coming back for more.
